Originally Posted by NWbluez06

What is the bases for asking this question? Is your P-car not stiff enough?

Originally Posted by msv

.

This purpose of this thread is not to start an argument (as it seems every thread is reduced to this...) about whether the stiffness is a problem, or if it is enough, I'm just curious.

Originally Posted by MAJ Z06

Can the frame be repaired?Yes!
http://forums.corvetteforum.com/show...9&forum_id=100

A very good SAE post from Runge Kutta:
http://forums.corvetteforum.com/show...e&forum_id=100
I thought I'd do several things simultaneously; mention some content of several
of the SAE papers presented at the recent 2005 SAE World Congress related to C6
including some interpretive remarks and mention some things that I'd like to see
one day.

1) Spread the aluminum frame across the entire C6 line. For that matter,
start designing SUVs with hydroformed aluminum frames. Just as most
engine blocks and heads are aluminum these days, we need a shift from
steel to aluminum frames. The aluminum C6 frame was mandated to drop 56kg
from it's steel C5 cousin. They got 62kgs out of it (down to 124.6kg). For some
reason, they INTENTIONALLY chose to not match the frame deflections of the
C6 steel frame but rather trimmed off 10kg instead. As is, deflections of
the aluminum frame without the magnesium roof structure are within 5% of
those for the steel frame. Apparently, the frame enters the Bowling Green
plant at 285 pounds and is 140 pounds lighter than the C6 steel frame.
(some of the numbers here are slightly inconsistent between papers)

[Imagine you have a coupe with the roof out. Measure the distance from
where the roof piece touches the windshield to where it touches the
corresponding back location where the roof piece mounts. I would
guess it's about 24-30 inches. Now put 2 400 pound guys in the car and
repeat that measurement. The frame will have bent (elastically) a slight
amount and the distance will be ever so slightly less. The difference in
the measurements is the deflection. In essence, if the steel frame were
to deflect 1 millimeter, the aluminum frame will deflect 1.05 millimeters.
That's basically what the mean by having matched the steel frame's deflection
to within 5%.]

By the way, the contract to Dana for the first year is 7000 frames. Also,
the side rails are not AA5754 but AA6063-T5 (4 mm). AA6063-T5 has a higher
yield strength but LOWER fatigue strength (at 10^7 cycles). My read on this is
that the vast majority of cycles are well below the fatigue strength of AA6063-T5
and a 5-10% loss in fatigue strength was worth the increased yield strength.
This increased yield strength probably helped the weight loss (AA6xxx alloys
help weight loss more than AA5xxx alloys):

http://msl1.mit.edu/msl/meeting_041...onstantine.pdf/ (page 12)

http://www.autoaluminum.org/downloads/corpub.pdf (See tables 2 and 6 in Appendix
______A. Fatigue strength correlates with ultimate tensile strength in these alloys)

It looks like the choice of materials also had to do with managing crash energy.

Ultimately, there are thresholds for both deflections and first mode frequencies.
Meeting these values may require putting back 10kg of aluminum alloy mass but I
doubt it. By the way, again, the aluminum frame used a good bit of tooling
that is used for the steel frame. Extrusions (21) were made from AA6063-T5,T6 and
AA6061-T6 (54% by mass) while sheet metal panels/stampings (63) used AA5754-O
(36% by mass) and castings (8) used A356-T6 (10% by mass). My read on this 10kg
issue is that in designing the steel C6 frame, some compromises were made to allow
a more optimal aluminum frame design (optimal designs for each frame material
would result in very different frame details). I think the steel C6 frame
is a bit overdesigned for not just the coupe but the convertible also. Besides,
GM can ill afford to be in the business of boutique aluminum frames. Hib Halverson
and a banned member (WhiteIce, BlackIce, CFour, C4FantaC, etc.) said, a year ago,
that the aluminum frame goes across the C6 line in MY2007. The GM engineer I spoke
with about the frame apologized for having to be so vague about the frame details.
A few other tidbits. The final Z06 frame including the magnesium roof structure
is 97% as stiff (frequencies not force per unit displacement or moment per unit
angular rotation) as the steel C6 frame. It appears that the fixed magnesium roof
structure increased the first mode frequencies by about 4%. As an interesting aside,
if the frame weighs 285 pounds and 54% of the mass is extrusions and most of
the mass in extrusions is included in the two side frame rails, then the two side
rails weigh about 154 pounds. Therefore, each likely weighs about 75 pounds or so.

For a bit of history, Dana was given a contract by GM for work on this aluminum
frame back in October 1999. Concurrently, within GM there were some early
publications and patents heading in this direction.

[September 24, 1996]

http://patft.uspto.gov/netacgi/nph-...RS=PN/5,557,961

and a closely related SAE paper [September 1999]

http://www.sae.org/servlets/product...CD=1999-01-3180

I don't know when ALCOA was brought into the process but it appears to
have done the initial design of the frame. One of the key design goals
of this frame is that the new aluminum frame must be integrated into
the C6 assembly process with minimal disruption, i.e. seemless integration.
All interfaces must match the steel frame.

Another thing to remember here is that the loss in stiffness of the frame when
it is built up into a full C5 or C6 is influenced by the stiffness of the
subsystems for the vehicle (C6 has a stiffer rear composite structure) as well
as the the mass caught up in the front and rear overhangs. C6 loses less stiffness
than C5 upon building the full vehicle. (The frame doesn't really lose stiffness.
The first mode frequencies of the frame are generally much higher than the
full vehicle because of all of the stuff now attached to the frame. It is this
difference to which I refer.)

The frequencies that were mentioned by DETLTU were a bit misleading.
The numbers 22.9Hz (bending) and 28.3Hz (torsion) were the program objectives
but the final numbers were 4% higher. Also, these numbers were not for the
frame alone. The are the frame, the entire roof, the windshield, the entire
rear of the car behind the driver minus the drivetrain, and parts of the front
fenders. That is my best guess from the picture. DETLTU also gave some numbers
for the steel frame but I see no mention of them anywhere.

Compare this with the SUV frame Ford studied in SAE 2003-01-0572

http://www.autofieldguide.com/articles/050303.html (scroll down 90% )
http://www.sae.org/servlets/product...CD=2003-01-0572

They got a 44% weight reduction if they had dimensional freedom but
only 20% if they did not. GM got 140/(285+140)= 32.9% with a 5% increase
in deflections at the roof and an essentially interchangable part. Also,
the "steel" C6 frame, I thought, already had a few aluminum parts, unlike
the C5 frame.

I predict C7 uses largely this same aluminum frame but the side rails will
be enlarged 20% or so in cross-section to take full advantage of the
aluminum. There may be a simple way to get some carbon fiber into this frame.

See:

2005-01-0095 : Crashworthiness of High and Low Pressure Hydroformed Straight Section Aluminum Tubes
2005-01-0465 : 2006 Corvette Z06 Aluminum Frame
2005-01-0466 : 2006 Corvette Z06 Aluminum Frame Engineering and Design Technologies
2005-01-0467 : Design Enhancement of the Rear Composite Structures for the 2005 - 6th
______________Generation - Corvette
2005-01-0470 : 2006 Corvette Z06 Aluminum Frame Manufacturing Technologies
2005-01-1392 : Aluminum Tube Hydroforming: Formability and Mechanical Properties
2005-01-1388 : The Warm Ductility of Commercial Aluminum Sheet Alloys

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2) Since titanium is still rather expensive and the new process technologies
like FFC don't appear to have reduced the prices yet, big pieces seem out
of the question and magnesium usage needs to increase rapidly. Both C6 crossmembers
should be converted to AE44 (a magnesium alloy used in the Z06 front crossmember).
The slight increase in NHV [Noise, Vibration,& Harshness], the one undesirable
result, is quite likely a nonissue with most C6 owners.

http://www.sae.org/automag/material...1-113-4-106.pdf ( Page 4 )

Other places to use it are:

Interior: Instrument Panel, Seat Components, Trim Plate
Body: Inner Door, Door and Roof Frame, Sunroof Panel, Bumper Beam,
___Radiator Support, A and B Pillars, Inner Decklid/Hood, Outer Hood/Fender,
___Outer Door, Dash Panel, Frame Rail.
Chassis: Wheels, Engine Cradle, Subframe, Control Arm.

That rear crossmember is likely to be worth nearly the same mass savings as
the front (5.5 kg = 12.1 lbs). The front crossmember/engine cradle is the
first production part from the USCAR team (fast-tracked).

http://www.uscar.org/Media/releases/castmagnesium.html

It may be too early for them to also have a rear crossmember for any C6
model.

See:

2005-01-0337 : Magnesium Engine Cradle - The USCAR Structural Cast Magnesium Development Project
2005-01-0340 : Development of the 2006 Corvette Z06 Structural Cast Magnesium Crossmember
2005-01-0734 : Wrought Magnesium Alloys and Manufacturing Processes for Automotive Applications

Still, I'd certainly be willing to pay extra for a titanium exhaust or titanium half-shafts.

http://www.webs1.uidaho.edu/imap/Fi...20in%20Auto.pdf

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3) What's the holdup with the polycarbonate rear hatch? The Mercedes C230 Sports
Coupe hatch-back is already using Exatec's polycarbonate technology.

http://www.apreport.com/pub/intervi...s/184151-1.html

The current one in the coupe and Z06 weighs 23.08 pounds. There is
11 pounds of high Cg mass to shed.

http://www.google.com/search?num=10...ing+automotive+

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4) The LS2 needs an analog to the LS7 heads. Keep the titanium valve springs
but use steel valves if they must. Drop the lift from 0.591 a bit and they'll still
easily outflow the current LS2 heads. By the way, an LS2 sure is cheap ($5495):

http://www.sdpc2000.com/catalog/120...ne-Assembly.htm

Now that the 4L65-E is history and the number of 400+hp cars grows, it's time
for more juice out of the LS2. It would help base model owners worry about
a new Carrera S, a 6.L Hemi, or a GT500 a bit less.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

5) Put the Z06 CHMSL on all C6's. It reduced lift of the Z06 by 79 pounds at
186 mph. The Cd for the 2006 Z06 is 0.342, this is identical to the value
for the 2004 Z06. At 186 mph, the 2006 Z06 has 1337 pounds LESS lift than
the 2004 Z06. The lift experienced by the car is very symmetrical relative
to the front and back of the car. Front brake cooling flow on the 2006 Z06 is
400% more than the 2005 model. Rear cooling flow is 200% of the 2004 Z06. The 2006
Z06 is 15mm lower than the 2005 C6 (0.60 inches).

See:
2005-01-1943 : 2006 Chevrolet Corvette C6 ZO6 Aerodynamic Development
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

6) The sulfur is almost out of the gasoline (30ppm by 01Jan06 in all but
several small regions like Montana and Idaho). It's time for LS7-type
heads with high pressure, direct, side injection. Speaking of DI, where
are the 3V heads with Orbital's low pressure, air-assist, central injection??
01Jan06 is 8 months away.

http://www.orbitalcorp.com.au/orbit.../dioverview.htm
http://www.orbitalcorp.com.au/orbit.../automotive.htm
http://www.delphi.com/pdf/techpapers/2003-01-0062.pdf

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

7) At the risk of dropping the mileage into gas guzzler territory, put
a 6L90-E behind the LS7 as an option. If the engine has DI then there will
be no gas guzzler issue. It'll never happen but it would be a great car
to own.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

8) It looks like the 6L80-E is about 34 pounds heavier than the 4L65-E. I
wonder if GM is going to try to offset this gain by dropping 34 pounds
out of the rear of the car for 2006. The rear hatch is a good place to get a third
of that back. Next, use the Z06 floor panels for another 6.22 pounds. A magnesium
rear crossmember would be worth about 12 lbs more.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

9) If there is going to be some MY2007 or MY2008 C6 that fits the description
given for the Blue Devil then front end weight addition will be a concern. As
I see it, you can turbocharge it, supercharge it, run a 3V design, or add
direct injection. Depending on how lean you want to run your DI will dictate
how much after treatment is needed. Still, I bet a 3V DI engine or even a
2V DI engine can get the 7.0L engine to over 600 hp with minimal weight
increases and still not get hit with the gas guzzler tax.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

10) The Milford Road Course was designed based on an assessment of the more
favorite features of:

Grattan Raceway, Virginia International Raceway, Spring Mountain Motorsports
ranch, Mid-Ohio Sports Car Course Watkins Glen International, Road Atlanta,
Putnam Park Road Course, Mosport International Raceway, Sebring International
Raceway, Gingerman Raceway, Road America, and Nurburgring Nordschleife.

2005-01-0385 : Design of the Milford Road Course

describes this course in detail including the 18 turns and several alternate
courses. While they do not use the phrase "toilet bowl," I assume this
refers to turn 6. This turn resembles the Karussell turn at Nurburgring.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

As best as I can tell from these papers, the carbon fiber fenders saved
3.03kg - 1.20kg = 1.83kg each (this may be a subset of the full fender
as the paper also states that the weight loss is 3kg per fender), the
front wheelhouse outer panels saved 0.73kg each, and the floor panels
saved 4.74kg - 3.33 kg = 1.41kg each. From earlier papers, the 2004
Z06 hood saved 7.9kg (or 56%) over the regular C5 hood. Just like the
aluminum frame articles, the production goal is 7000 cars per year.
The fenders are made by Vermont Composites Inc.

http://www.vtcomposites.com/performance-automotive.htm

The floor panels are made by

http://www.mfgresearch.com/intranet.htm

By the way, one kilogram equals 2.204622 pounds-mass. If the production
capacity is there and the price differential is minimal then the floor
panels could be put in the coupe and convertible to save 2.82kg=6.22 pounds.
It is clear from many different articles that the emphasis was on front end
weight loss. I wouldn't be surprised to see a CF hood on the Z06 soon.

2005-01-0468 : 2006 Corvette Z06 Carbon Fiber Fender Engineering, Design and Material
Selection Considerations
2005-01-0469 : 2006 Corvette Z06 Carbon Fiber Structural Composite Panels Design, Manufacturing
and Material Development Considerations

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

12) I copied these also but I don't have much to say about them. The DI
paper is about 4V engines.

2005-01-1854 : The Supercharged Northstar DOHC 4.4L V8 Engine for Cadillac
2005-01-1937 : Combustion Characteristics of a Spray-Guided Direct-Injection
_____ Stratified-Charge Engine with a High-Squish Piston

Papers on the Northstar engine (3) are much nicer papers than the rest. The authors
spend much more time on them.



http://forums.corvetteforum.com/show...8&page=1&pp=20
How to Lose 136 lbs.

By John D. Stoll

Ward's Auto World, Jun 1, 2005


Hopkinsville, KY, is in the racehorse business.

Located in the heart of Kentucky's bluegrass pastures, this city of 31,000 people boasts its share of thoroughbred racehorse breeders. Each day, the pounding of hoof beats lends plenty of rhythm to daily life.

In July, that sound will be rivaled by thumping heartbeats at a local 410,000-sq.-ft. (38,000-sq.-m) Dana Corp. frame plant, as it hits full stride in an effort to churn out annually 7,000 of the most-advanced structures ever to underpin a General Motors Corp. vehicle.

The plant continues to build GM fullsize van frames and stamp out parts for Toyota Motor Corp.'s Princeton, IN, truck plant. But this summer it adds Hopkinsville's newest breed of racehorse: The 285-lb. (129-kg) fully aluminum Corvette Z06 spaceframe.

The new spaceframe represents several significant firsts for Dana: Never before has the supplier had primary design responsibility for a frame; it is Dana's first underbody made entirely of aluminum; and it employs the most liberal use of laser welding — 46 ft. (14 m) worth — on a Dana frame.

Dana hopes to replicate the process for GM or other OEMs looking to differentiate a low-volume (10,000 units or less) vehicle program with a unique underbody, Gilberto Ceratti, president-Structural Solutions Group, tells Ward's.

Materials such as aluminum are seen adding sex appeal to high-margin vehicles, such as those playing to the high-horsepower supercar crowd.

“One key advantage for this design is for low- and medium-volume vehicles,” Ceratti says. “We can make it reasonable for the customer due to a much lower investment (on their part).”

While auto makers strive to keep underbodies as common as possible to save money for visible differentiation, going with a lighter-weight chassis for low-volume performance models could provide derivatives without breaking the bank.

In the Corvette's case, a less-expensive steel frame built by GM holds together the standard model, introduced in '05, while Dana's aluminum carriage handles the demands of the '06 500-hp Z06 — said to require more torsional rigidity and lighter weight than its stable mate.

GM approached Dana four years ago with the task of creating an aluminum frame that would mirror the standard steel frame so the two could share the same assembly line with little process variation.

Ceratti says Dana's proven frame record, combined with can-do determination and a commitment to hitting cost targets, won the business.

“What really drove us here was the innovation and technology,” says Mike Laisure, president-Dana Automotive Systems Group, pointing to the Z06 program as a platform for profitable aluminum frame production or chassis components in the future. He concedes, however, the low-volume Z06 program is not profitable for Dana.

“As we move it into the higher volumes, the intent is it will help us improve margins,” Laisure told reporters earlier this year. “Obviously we're in this to make money, not just show off our capability.”

Hybrid trucks may be the biggest opportunity for Dana to expand its aluminum frame business, company sources say.

Brett Deep, GM's project manager on the program, says Dana is prancing out of the gate, having exceeded GM's targets so convincingly (including coming at least 5 lbs. [2.26 kg] under weight) that he's already moved onto a GM truck program with less than two months until the Z06's Job One.

“There are no issues,” he insists.

B.J. Kroppe, director-Dana Structural Solutions product engineering, says Dana succeeded under the motto, “Same as steel.” Same, but different. The Z06 frame boasts at least one major difference: It weighs a crucial 136 lbs. (62 kg), or one-third, less.

Alcoa Inc. brought its expertise from the Ferrari 360 Modena's aluminum spaceframe to Dana's design studio and helped the Toledo-based supplier bang out an aluminum frame that looks nearly identical to the steel one.

Hopkinsville, less than a 90-minute drive to GM's Bowling Green, KY, Corvette plant, is uniquely positioned to initiate the spaceframe revolution at Dana. During a tour, Plant Manager Jerry Bieck says the facility repeatedly has won quality awards and has a laser-weld expert (shared with Dana's Ford F-150 frame plant in Elizabethtown, KY,) on hand to assist with the new technology.

The entire tunnel assembly is laser welded in a high-dollar laser booth that promises maximum efficiency and spot-on accuracy with difficult-to-weld aluminum, according to Dana officials.

In fact, the 21-34 people working on the niche frame line (depending on workload) are themselves laser-weld experts. Bieck says qualified workers — “regardless of whether they're manually welding or not” — had to complete four hours of classroom training specifically for aluminum welding, including mastery of MIG welding; undergo four hours of hands-on training; pass a written test; and complete a manual welding test with 100% accuracy.

“There cannot be any flaws whatsoever” in the laser welds, says Bieck.

The training was extended to each Z06 frame line worker, because Dana wants to have flexibility to plug in players as they are needed, Bieck says. The absence of union representation in the plant undoubtedly plays a role in Dana's ability to flex its workforce.

One thing missing on Hopkinsville's assembly line: spot-weld guns. Dana opted to use 236 self-piercing rivets (SPR), priced at 3 cents apiece, as a bulletproof alternative to spot welds.

GM's Deep insists the SPRs are far more effective joiners, not requiring pre-drilled holes or sealers to fill any gaps. He says SPRs are easier to monitor for quality.

“When you hit a rivet, you know it's there,” he says, pointing out it is virtually impossible to misfire a rivet into the aluminum structure given the tooling used. The rivets hold their ground better in a crash, don't require electricity (air guns do the job) to install and take the same 3-second cycle time needed to produce spot welds.

The aluminum frame requires about 18 minutes to build, with much of the time devoted to precision machining on a 5-axis, high-speed computer-numerically-controlled (CNC) machine located near the end of the line. The unit measures the spaceframe, drills necessary holes, rolls threads and perfects the critical interfaces, including the upper control arm and roof bow cover.

The CNC machining is essential to crafting the Z06 frame to mirror the base Corvette's, so the two can run down the same assembly line with as few variations as possible.

“It basically has the ability to machine within a quarter millimeter plus or minus,” Deep says. “We've used it to basically get this frame exactly like the steel one.”

Of the 1,777 parts that make up a Corvette, only 11 interface differently with the Z06 than they do with the base model. The magnesium roof, the battery (placed in the rear on the Z06 for weight distribution reasons) and the rear upper control arms are among the critical differences, Deep says.

Hanging the Corvette's fiberglass frame off both aluminum and steel posed a challenge. Dana solved it, dipping the aluminum frame in phosphate and then coating it with a substance that adheres to the fiberglass.

At least one point of differentiation speaks to the utility of aluminum: The rear suspension attachment, placed just aft of the integrated aluminum B-pillar, is a 1-piece casting that is fabricated on the CNC machine. On the traditional steel frame, it is a 5-piece component, welded together and requiring five different sets of tooling.

A similar reduction was achieved with the hinge pillar subassembly.

While this doesn't make the aluminum frame anywhere near as cost effective as the steel unit, it promises improved quality, less upfront tooling and simplicity. Such efficiencies will be necessary if aluminum is going to move beyond niche status.

Deep says GM currently is building a competitive advantage with aluminum, thanks to the Z06 frame project.

“We put a 1-piece aluminum casting on the (steel-frame) convertible as a seatbelt retractor roller assembly instead of four stampings. We did that leveraging what we learned working with aluminum.”

Look for more aluminum know-how from GM in the future thanks to the Dana partnership, Deep says.
— with Tom Murphy

From a GM engineer on the AL frame.
--------------------------------------------------------------------------------

I asked him about converting a Z06 to a vert and about the tunnel plates.

Todd,
Not to be too vague, but printed response can sometime come back to plague engineers in this field.

The Al structure was design to meet or exceed Steel spaceframe torsional rigidity and bending. This was achieved by distributing some of the loads up through the upper portion of the structure (i.e. Al windshield Frame, Magnesium Roof, and Al roof bow). For this reason, if these item were removed, a reduction in rigidity would be expected. While I am not surprised that the aftermarket world has addressed Z06 hardtop, I am not familiar with the aftermarket components. I suppose with substantial structural reinforcements, these companies may be able to gain back some of the rigidity lost, I could not speak the exact amount lost (as we never tested the vehicle without the roof structure). The Z06 has always maintained its racing spirit by providing a closed roof structure.

While a open roof Z06 is a neat idea, I would suggest a 2006 Corvette
Convertible, designed for an open roof environment. The Convertible has a great deal of performance and a heck of a lot of fun to drive.

Same goes for the tunnel structure (don't know what they would do for the spaceframe. But, the spaceframe has a patient on it for a reason. The tunnel portion is a closed box section from the 3 sided Al tunnel top and the Al tunnel close-out (attached with 36 fasteners).
Who knows what a little extra steel will do ... add mass??


A few threads discusing the frame:
http://forums.corvetteforum.com/show....php?t=1388625
http://forums.corvetteforum.com/show...m&forum_id=100
http://forums.corvetteforum.com/show...m&forum_id=100
http://forums.corvetteforum.com/show...m&forum_id=100