In the one that I know about, those are castings, and they are attached to the adjacent parts by a combination of adhesives, rivets, and folding the edges of adjacent steel panels around the edges of the aluminium part to encapsulate the adhesive and then spot welding the assembly in place. Tesla has something like this in production although that's not the one I've looked at.

Thanks for confirming this exists at least. It still strikes me as an odd materials choice for that particular place/application.

Are there a lot of attachment points? If so then maybe the aluminum is there just to have some material near the areas of attachment.

The strut tower and the area just forward of it tends to be a complicated structure welded together from several smaller pieces. Doing it as a casting lets a bunch of that be built as one piece and yet incorporate even more attachment points for odds and ends like battery, windscreen washer bottle, coolant reservoir, electrical distribution block, etc. You'll notice that the rail structure underneath it - which is part of the frontal crash structure - is still steel. The curved structure above it, also steel, is for low-offset frontal impact.

Apparently that's a 2015 Volvo XC90. One solution is Atlas Copco BG Rivets.

Cheers

Greg Locock


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FSW solutions for bonding aluminum and steel panels do exist, but I think 2015 might have been before that technology was really volume production ready.

Honda pioneered aluminum frames in their off-road motorcycles in the 1990's for this very reason. They used castings in the complex areas of the frame such as the head tube and sub plate. They were able to produce the entire frame with some 7 welds if I remember correctly.

Thanks for your insights. The use of a casting seems logical (for the versatility of attachment points), but I am still unsure if aluminium is the best choice of material for this (for fatigue reasons). But, I am sure those who decide in this know better then me...

Well... aluminum has been in use in automotive structures for a looooong time at this point. How many fatigue failures of automotive structural components have you seen or heard about?

I'd say the use of aluminium alloys in body in white is minimal so far, so that statement isn't really a good representation of the situation...

Aluminum BIW components have been in use for more than 20 years.. this isn't a recent development

Ahem. Panhard Dyna X. 1948-54. 47000+ built. Also of course every LandRover.

Cheers

Greg Locock


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Lots and lots of cars and trucks have aluminium control arms in the suspension.

Aluminium complete unibody: Tesla Model S, Model X, some high-end Audi models, the original Honda Insight, the original Audi A2 minicar.

I own three motorcycles that have frames and swing-arms made of aluminium, generally welded together from a combination of pressings and castings. The steering neck, and the rear suspension attachment points, are rather high-stress areas. This has been commonplace since the 1980s.

As far as this particular Volvo unibody goes, the loads on an upper strut mount of a MacPherson strut suspension are reasonably predictable. The front crash-bar is designed to absorb energy by deformation once; the stresses imposed upon that part during normal use are negligible.

If you really want to question the industry's judgement, consider the common use of glue as a fastening method.

... a.k.a. "structural adhesives". Not exactly Elmer's school glue.

If you drive a car that has been built in the last 3 or 4 decades, the windscreen and rear window are glued in. Before that, they were just held in place with a funky-cross-section rubber gasket.

Not to mention that the 'glue' we're talking about in this case makes a joint that is stronger than a weld on day 1 and stays that way through the entire life of the assembly...

Anyone cares to guess what part of all BIWs in general, consists of aluminium?
For the thousands of Panhards there are millions of other cars without aluminium, so I am not really convinced (yet) that "no fatigue failure reports" really means something.
And yes, I am well well aware of structural bonding, have more than once done the comparison between welded and bonded joints and adhesives certainly have their particular advantages.

Quote (kingnero)

aluminium seems not logical, but on the other hand I have zero experience in car frame, unibody or chassis design

For someone who said this in their original thread, you seem awfully determined to disagree with a bunch of people who know these types of assemblies intimately

Suffice to say that fatigue analysis is sufficiently understood for car makers to build chassis in most materials. Lotus Elise appeared in 1996 with full aluminium, adhesive-bonded chassis. Elise production continued for 25 years (Lotus still makes other models using the same technique) and there are plenty of 25 y.o. Elises still going strong.

je suis charlie

Quote (kingnero)

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, ...

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.

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.

Quote (kingnero)

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:

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.

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-20...

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.

Quote (kingnero)

@ 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.

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