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Do you think C8 will have all C/F body panels?

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Old 05-15-2018, 10:16 AM   #41  
elegant
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Thank you acrace. Always good to learn more even if not for our Corvettes.
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Old 05-15-2018, 10:26 AM   #42  
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Thank you acrace. Always good to learn more even if not for our Corvettes.
The CarbonPro is an innovative use of a new form of carbon fiber and it may trickle into other GM platforms (I have no insight). But if you find the intro video with interviews, one of the lead engineers (EGM) has a long history on Corvette.

And for the Raptor, it is a case of CSP adapting the TCA material developed for C7 and finding a new customer/application.

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Old 05-15-2018, 11:21 AM   #43  
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Some body panels are just for aerodynamics, why make them out of something light and strong and expensive, make them out of something light and cheap.
That's about right.CF is great...the best material around.Unfortunately, it is still expensive (getting cheaper though).We're just not there yet on having CF mass produced for consumer cars.Someday, we will.When that day happens, we will be able save a lot of fuel with the lighter cars...and that's a good thing.
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Old 05-15-2018, 03:18 PM   #44  
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I looked at the video and to my eyes, it looks too textured to create a paintable finish, such as for an exterior body panel. However, it seems great for internal parts of pickup bodies and other applications.., e.g. lighter weight and strong.

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Old 05-15-2018, 04:04 PM   #45  
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I looked at the video and to my eyes, it looks too textured to create a paintable finish, such as for an exterior body panel. However, it seems great for internal parts of pickup bodies and other applications.., e.g. lighter weight and strong.
Agree with you, I think that's why the pickup box inner works for this material (Sereebo) but it shouldn't be used for Class A exterior parts.
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Old 05-15-2018, 04:15 PM   #46  
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I don't think CF/ composite body panels hardly cost a thing to produce, after the expensive molds and what not are built.

GM installs CF fenders on a C6Z, but could have saved 25# for $40 (OEM cost differential) on a Li battery, but they don't. Why? cause the battery cost more than the fenders and is harder to implement imo.

The new GM trucks have a CF/ composite bed (which is huge and complex) and it's like a $850 option at the dealer level.
According to Plasan, who makes the carbon fiber hood, roof and roof bow for the C7, part production cycle time is 9 minutes.

According to CSP, who makes the hollow spherical glass filled SMC panels for the C7, the part production cycle time is from 2.0-3.5 minutes.

That's why carbon fiber parts costs more than hollow glass filled SMC.

Carbon fiber----6.7 parts per hour production rate.

SMC------------21 parts per hour production rate.

Also, with the slower part production rate, means that additional expensive molds are required to meet the required number of parts per day. One very expensive mold can produce three times of parts per hour in SMC vs carbon fiber.

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Old 05-15-2018, 05:39 PM   #47  
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JoesC5 has a good review of the challenge for carbon in volume automotive adoption, and frankly of composites in general. Think of aluminum or steel stampings - a hit every 5 seconds or so. Granted, you need progressive (multiple) dies for metal stamping, but the fast cycle times can overcome the tooling capex quickly for decent sized production volumes.

To help with composites pricing understanding, typical glass SMC panels would be 25 to 45% glass fiber, 5 to 20% fillers (including glass spheres), and the rest is a vinylester or polyester resin. Market price for glass fiber as used in SMC is under $1/pound. Vinylester/polyester resin pricing can be $2.50 to $5/pound for a ballpark number.

Comparatively, carbon fiber panels are typically 55% to 65% carbon fiber and the rest would be resin, usually an epoxy of some sort. Large tow carbon fiber would be approx. $9/pound and epoxy is in the small general range (probably a little higher) as a starting point.

(All prices approximate, but reasonable for the purposes of this forum)

You can do the math, and add in JoesC5 numbers on cycle time, and the economic story can be told.

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Old 05-15-2018, 05:43 PM   #48  
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Oh, one thing that I didn't think of . . . in JoesC5 "study" in post #46, not only would one have to consider tooling, but also equipment capex becomes a consideration. Since JoesC5 mentioned Plasan, they had a new process that required new equipment - processing equipment, material handling equipment, and they had a greenfield site. That does become a consideration when amortizing over Corvette (low) volumes.
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Old 05-15-2018, 07:59 PM   #49  
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The 2014 and 2015 SMC panels on our C7’s were 24.9% glass fibers; the 2016+ SMC body panels are down to 20-21% glass fibers.
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Old 05-15-2018, 08:35 PM   #50  
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Default Carbon Fiber use on the C7

The C7 (and likely the C8) is NOT a classic monocoque or semi-monocoque structure - all the loads are carried by the aluminum frame. Consequently there is little benefit for C/E skins, and in fact the fasteners which tie the skins to the frame DO NOT transmit sheer loads by design. The only places where C/E really buys its way on are large integrated unitized panels - ie the roof and the hood, as well as grafted on aerodynamic surfaces, such as the front lip spoiler and the rear wing on the ZR1.

The lighter and thinner they can make SMC panels, the better suited they are for this car, since nice they are not really structural. BTW, the Porsche 917 was built largely the same way - large fiberglass panels for aero., laid over a welded tubular space frame. It made for a very light, very fast car, however they were not crash-resistant. Porsche only went to unitized C/E tubs for the 956 and 962 when the ACO and other sanctioning bodies forced them to make their cars more crashworthy.
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Old 05-16-2018, 02:32 PM   #51  
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I was under the impression that the use of the low density SMC(Hollow spherical glass filler)was first used on the 2016 C7 to reduce weight(20 pounds).

I discovered that the use to the low density SMC was first used on the C5, on the roof panel on the fixed roof coupe(later to become the Z06). Savings of 6 pounds on the roof panel.

Whereas the regular SMC panels had a specific gravity of 1.8 to 1.9 g/cc, the low density SMC has a specific gravity of 1.3 to 1.4 g/cc. Aluminum has a 1.2 g/cc.

The calcium carbonate used in the regular SMC panels has a density of 2.7 g/cc and the hollow glass spheres used in the low density SMC has a density of 0.37 g/cc.

I believe that SMC with around 0.98 g/cc is under development.

The molding rate of the roof panel for the fixed roof C5 was every 3 minutes for 160 roofs in an 8 hour shift.

Carbon fiber is around 40% lighter than aluminum, and 35% lighter than magnesium alloy, but all three are more expensive than SMC.

Last edited by JoesC5; 05-16-2018 at 02:33 PM.
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