Rear seat pan design

[Chiefxxx]

Hello,

I am interested in BIW construction, and particularly the rear seat pan. I know that to reduce weight some manufactures now use magnesium. Does anyone know what the design requirements are for such a component? Where can i learn about what kind of conditions, temps and loads such a component needs to resist?

many thanks

Chief

 

[GregLocock]

I could believe a seat frame being made of magnesium, struggle a bit with a seat pan.

Anyway, typically OEMs measure these things.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[BrianPetersen]

To me, a "seat pan" is part of the welded structure of the bodyshell, which ordinarily precludes that part being anything other than a sheet steel stamping, or in some exotic cases where the entire bodyhsell is aluminum, a sheet aluminum stamping. Can't weld differing materials together, and trying to weld magnesium would be an interesting proposition.

With a good many cars nowadays, the thing that's on the other side of that seat pan (i.e. underneath), is the fuel tank - another reason to not make that out of something that can catch fire.

 

[Chiefxxx]

Hello again,

It maybe that I have asked for the wrong item. I know what the part is called in German, its the tanktrennwand which translates to tank partition wall. I am particularly interested in the materials used to construct this in the mercedes e class and how what loads it might have to withstand.

Any ideas anyone?

 

[BrianPetersen]

The translated phrase is not meaningful in English (or at least, not to *this* English speaker). Where is it in the vehicle, and is it part of the welded structure?

Your question concerning "body in white" suggests that no matter where this piece is, it is part of the welded structure. The "body in white" is all the stampings welded together, and the same comments still apply: Any part of the "body in white" has to be a material capable of being welded to the adjacent parts. If the "body in white" is steel then all the individual parts have to be steel. If it's aluminum, then everything has to be aluminum.

If you are talking about something else, please explain it.

 

[GregLocock]

There was an old soluble aspirin TV advert the punchline of which was Plink Plink Fizz.

That is the approximate result of dropping magnesium into salty water. I find it very hard to believe that an exterior part of a production car would be made fom magnesium, given that many markets salt their roads in winter.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[CoryPad]

Volkswagen Lupo had a magnesium rear hatch outer panel:

http://papers.sae.org/2000-01-1123

Modern magnesium alloy corrosion behavior (and thermal behavior) is much different than basic laboratory experiments.

 

[GregLocock]

Wow. OK. I was testing epoxy coated AZ 61 (I think) in seawater.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[GregLocock]

Although note that the magnesium is the inner frame for the hatch, not the outer skin.


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[CoryPad]

Yes, it was the inner panel, but it is exposed to the elements more than most application. VW tested the Mg panel extensively for corrosion resistance. Ford also did extensive corrosion resistance for Mg parts, for example:

http://papers.sae.org/2009-01-0037

 

[patprimmer]

For years, most VW beetle gear box housings ans some model crankcases where magnesium alloy. While they showed some corrosion it was never enough to be a problem. Emphasis I think might be on alloy.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[RomeoReject]

Or consider that Ferrari FXX has rims which are 85% magnesium, or that a Porsche Carrera GT has a transmission case made from magnesium. Both are exposed to the elements (The Porsche's transmission is directly under an exposed vent) and both handle it just fine.

As to the original poster, still a bit confused as to what part you're asking about. Why not find a picture and circle it for us?

 

[NickJ67]

Those early VW engine and G/box casings may not have corroded too badly, but they do burn really well. As a kid in Africa I witnessed a fire causing the total destruction of an early 60s VW Kombi and once it got going.... wow! Talk about hot and bright! When they hauled the shell away they didn't sweep up at all and the engine and gearbox internals were left, like the skeleton of some strange animal in a patch of bright white powder. The crank, rods and barrels were there and I seem to remember some of the heads were still present but very melted so presumably they were aluminium. I'd be quite wary about the use of magnesium alloys on anything I was going to ride in!

Nick

 

[patprimmer]

All air cooled VW heads where aluminium alloy.

The gear boxed are actually very difficult to ignite, but once started they really go off. I must admit I tried to burn a broken one to see the display. A match evnm on a sharp edge would not do it. It took an oxy acetylene flame.

Despite my relative youth at the time, I lacked the courage or perhaps had the good sense not to aim a jet of pure oxygen at it after it was burning.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[Chiefxxx]

Hi guys,

Very sorry for the delay, but i now have more information about the part in question. SO I believe that the part sits in the rear of a 2 seater roadster prodcued by Mercedes. I have attached a picture of the part which is in composite, i found this picture on the web. Anyway I am interested, in what the design requirements are for such a component and what the actual industry name is for it. A descriptive specification would be great.

If anyone can help I will be grateful.

Cheers

 

[WhizzMan]

Regardless of design and safety requirements and regulations, you don't need the same material used in the entire body. Modern cars don't depend on welding as much as they used to. It is now very common to glue on panels that have a structural function, or even glue beams in some cases. This allows for various "space age" materials to be used. Notably, the Lotus Elise was the first production car to have a complete chassis/body glued together out of aluminium beams, no welds used for the beams at all.

Regarding the fire resistance of materials: steel will burn just fine, it will just take a higher temperature to ignite and usually requires external heat sources to maintain a flame. Using flammable materials on cars is done all over, it's just a matter of how much coating and retarding material used for these to be deemed safe. The entire interior of almost every production car is actually quite flammable. I wouldn't overly worry about some magnesium used in a panel that is not close to the engine, high electric current or brake heat.

 

[DanEE]

re: "The entire interior of almost every production car is actually quite flammable."

Having been involved in some testing of plastics involved in a fire, some years ago, certainly agree with this..

Anyone who has seen ABS plastics and other synthetics first melt into a black tar like substance from adjacent flames, then ignite with the vigor of petroleum is convinced. This was with "flame retardant" compounds added which gives off bromine and chlorine gases when burned..

I now view the interior of my car as having a nice, comfortable coating of petroleum.. not the place to be in a fire.

Majority of plastics are after all, a petroleum by-product.