Front suspension turrets in aluminium, in an all-steel unibody? 1

[kingnero]

Just saw the above image on LinkedIn.
As a welding engineer, I'm wondering:
1) is it correct, that the fromt suspension turrets are in aluminium, (cast/deep drawn?)
and if so,
2) how are they connected to the steel frame (conventional welding isn't an option, that leaves deformation joining, fastening using bolts or rivets, adhesives, ...) ?

I'd say these are fairly high (cyclic) loaded parts, so aluminium seems not logical, but on the other hand I have zero experience in car frame, unibody or chassis design, so there's that if this is a stupid question...

 

[BrianPetersen]

Anyone cares to guess what part of all BIWs in general, consists of aluminium?

I am not sure what your question means.

Tesla has built something like half a million Model S and X over the last 10 years. Those unibodies are all-aluminium. If the entire unibody is aluminium then the attachment points for the suspension / subframe are ...

The Model 3 and Y unibodies are mostly steel but incorporate aluminium components, and they've built something like 1.5 million of those.

The Audi A8 has been around since 1993 with an all-aluminium unibody.

And, while the Ford F150 is a body-on-frame vehicle, that doesn't mean the bodyshell isn't subject to most of the same issues concerning how it's built and what stresses are imposed upon it. Those have been aluminium since 2015 and millions have been built.

Let's not forget that practically every aircraft structure is aluminium. Its fatigue behaviour has been analysed rather extensively, I'd say.

"why isn't every car made of aluminium, then"?

Because it's expensive. And after a collision, it requires specialist experience to repair them. Ford went through an enormous training and qualification exercise before bringing the aluminium F150 to market to ensure that there were sufficient shops out there who could repair them. Tesla refuses to even sell parts to anyone outside of their captive authorised repair-shops. Audi is Audi and they don't seem to care if the car is expensive to repair.

I drive cheap cars. They have stamped-steel bodyshells spot-welded together. I ride premium motorcycles. Most of those (not all) have aluminium frames and swing-arms. All have aluminium front fork outer housings, wheels, engine crankcases, pistons, cylinder heads, ...

 

[kingnero]

I would have thought it would be easy for a bunch of people who know these types of assemblies intimately to give some simple and clear arguments why these suspension towers are in aluminium instead of steel, but I see very few such replies.

I'm not arguing against aluminium, I'm trying to have a better understanding of "why" they do it that way.

@ Brian Peterson, "what part" == "which percentage" (as in, weight % or volume % or however it is noted). Does my question makes more sense now? I'm suffering from translation issues here.
I know there are quite some cars made from aluminium / with aluminium parts, but the (vast?) majority is steel. It would be interesting to know the distribution between both material groups. Few tens of thousands or even 1.5 million cars is nothing relative to the entire car industry.

 

[3DDave]

Why would you not contact the company that makes the car? Your question makes no sense as the answer is within a complex and costly design and manufacturability and sales study, likely costing 10s of millions of dollars to produce. You want that for free? LOL.

 

[SwinnyGG]

give some simple and clear arguments why these suspension towers are in aluminium instead of steel, but I see very few such replies.

You got that answer in the third response to your thread, and a more detailed version of the same answer in the 4th response. :shrug:

 

[enginesrus]

The only reason to use aluminum in an auto body structure is the make it more difficult to fix, especially an aluminum casting that will not respond well to welding. In the manufacturing world aluminum is desired because of the ease to cast, and machine. To come close to the same strength of steel in a highly stressed application the cross section of the aluminum parts needs to be increased to the point there is pretty much no weight savings.

 

[BrianPetersen]

No argument about the repair difficulty but the aluminium-body-and-steel-frame Ford F150 is 700 lb lighter than the corresponding steel version from the year before, of which 450 lb was from the body and frame (it isn't specified how much of each):

https://www.torquenews.com/106/ford-breaks-down-2015-f150-weight-savings

Aluminium sheets need to be about 40% - 50% thicker to achieve the same stiffness but it's a third as dense, leading to the comparable body-in-white weighing about half what the corresponding steel one does.

I have a customer that robotically MIG-welds aluminium bumper structures and "crash cans" together. You don't fix those parts, you replace them in a collision-repair situation. I have another customer that robotically MIG-welds aluminium <top secret very large parts that I can't talk about> together. Obviously there is a certain minimum material thickness for this to be viable. Aluminium sheet-metal body-in-white structures don't normally use welding. They're some combination of glued/riveted/hemmed/bolted together.

In Tesla's case, for the Model 3 and Model Y which use a multi-material structure, if you break the aluminium "gigacasting" in a crash, you've got a lot more to worry about than whether you can fix that part ... the car will be a write-off.

 

[BrianPetersen]

@ Brian Peterson, "what part" == "which percentage" (as in, weight % or volume % or however it is noted). Does my question makes more sense now? I'm suffering from translation issues here.

It is anywhere between 0% on the majority of light-duty cars and trucks, and 100% on those that use all-aluminium unibodies, examples of which have been listed above. An industry-average is not a meaningful number, since it would be affected by sales numbers of each relative type.

The number of aluminium-body Ford F150s built each year is not small! YES, I know it is only the cab and not the frame that is made of aluminium.

 

[CWB1]

There can be cost benefits to aluminum as well, both direct material and I assume indirect regulatory costs.