How would you manufacture a wishbone?

[zir786]

What manufacturing method would you use?
And how would they differ in a batch and continuous process? (making 100 vs 100K)

[Jersey Tom]

Let me guess.. for a kit car with custom suspension? Before I give my opinion, what do you think? What manufacturing processes are appropriate for small scale and prototyping, and which are more appropriate for large volume?

[mep]

Sounds more like formula student.

[Just_a_fan]

I'd subcontract it out to someone who knew what they were doing...

[tathan]

For making 100k I'd get sheet steel, stamp two and spot weld them together with the ball joints in. Cheap, stiff, low tooling cost.

For low batches, just make them by hand out of tubes.

[Greg Locock]

For high volume you might consider cast aluminium, especially given the cost of aluminium at the moment. I have seen cast steel used where appropraite as well, but of course both of those two need careful design to hit your weight target.

I doubt anything metal will match the strength, fatigue life and weight of MIG welded CroMo tubes put together by a good fabricator.

[Tommy Cookers]

I have seen cast steel used where appropraite as well,

I doubt anything metal will match the strength, fatigue life and weight of MIG welded CroMo tubes put together by a good fabricator.

I would assume that something that looks like cast steel would be (cast) ductile iron, possibly under another name or trade name
(what casting technique would be needed for steel ?)

some people might not know that when engineers mention CroMo etc they mean 'Chrome Molybdenum Steel'
and have in mind a well known (SAE ?) specification 4130 ?
most majorly industrialised countries have broadly equivalent indigenous specifications
eg for weldable high-strength alloy steel tubing not necessarily proclaiming these ingredients

not long ago 'quality' wishbones etc were forged

[Greg Locock]

I don't know much about the cast steel ones, Hitachi did the entire job.

[marcush.]

For making 100k I'd get sheet steel, stamp two and spot weld them together with the ball joints in. Cheap, stiff, low tooling cost.

For low batches, just make them by hand out of tubes.

You think a stamping tool of the size of a wishbone is low cost?

I´m pretty sure a casting will beat this with ease ...my suggestion :look how manufacturers of products with the same sort of production numbers tackle the job...

So if your production numbers are far above the 100k mark stamping make sense ..but for the lower range production numbers for example Porsche or Ferrari it looks like Aluminium castings or forgings .

Looking at the bicycle frame market it seems entirely feasible to do a TIG welded Tube job as well ..anyone seen a fully automated TIG welding job ?

http://www.youtube.com/watch?v=7zvynjK4s2g

The welding may all done in less than 2 Minutes ,add to this some 2 or three minutes of automated tube cutting and end finishing and you are in a jewellike finish endproduct at very low actual production cost .
You got a investment of a 5axis CNC mill to perform the end finishing and the welding robot ain´t cheap either ...but this would open the possibility to

use the machines for other jobs as well
very low specific tooling cost for the product ittself -ideal for subcontacting - and change as your product evolves...

Then ,if weight is not the primary concern but cost...you just go up a notch in wall thickness and crossection and leave the
expensive steels in the shelve.....obviously my approach will leave this road wide open in case you need to trim weight later on.

[tathan]

i didn't even consider casting a wishbone, i'd either forge aluminium or press steel because both will give consistent strength, unlike a die cast part which if you're making thousands you can't realistically inspect internally and you will get occasional ones breaking, unless you overspec it so much that you end up with a unacceptably heavy part.

Stamping sheet steel is definitely cheaper and easier than forging it - the tooling cost for forging big parts is astronomical.

[marcush.]

what about that one :thixoforging SMG Schuler has done some work with Audi and TRW in that area...
they claim it´s a lot cheaper than forging as you don´t need the high pressure and wear of the tooling is less..
it is possible to produce parts up to around 3kg of Mass and thickness of around 1mm -if that´s not making your day what is?

The paper is a bit older surprisingly and only German:

http://www.cct-bw.de/veroeffentlichung_ ... eutsch.pdf

[Jersey Tom]

i didn't even consider casting a wishbone, i'd either forge aluminium or press steel because both will give consistent strength, unlike a die cast part which if you're making thousands you can't realistically inspect internally and you will get occasional ones breaking, unless you overspec it so much that you end up with a unacceptably heavy part.

Define "unacceptably heavy." In a production environment, how important is component weight versus component cost?

[marcush.]

very important .
No OEM can do without Weight management and there is usually a tradeoff number cost per weight savings floating around
in development .

Volkwagen had already a few years ago even a Eco balance template to work out energy savings over product lifecycle to avoid falling into the trap to just go for lightweight and forget about the total cost from source to end /recycling ..

If I remember correctly for a weight saving of 1 Kg you could get a bonus(higher cost per part ) of around 3€ in 2009 (not VW).

so yes it is something continuously evaluated and targets are to be met. Usually this is a very conservative number and surprisingly with Catia and modern engineering methods one would think this is always a point landing -it is not .

Wasn´t the new DTM car 200KG overweight when first cars were build and they had to redesign the whole lot to be able to run it as the crash testimng was based on the original weight targets?

[Lycoming]

Looking at the bicycle frame market it seems entirely feasible to do a TIG welded Tube job as well ..anyone seen a fully automated TIG welding job ?

http://www.youtube.com/watch?v=7zvynjK4s2g

The welding may all done in less than 2 Minutes ,add to this some 2 or three minutes of automated tube cutting and end finishing and you are in a jewellike finish endproduct at very low actual production cost .
You got a investment of a 5axis CNC mill to perform the end finishing and the welding robot ain´t cheap either ...but this would open the possibility to

You can use special laser cutters for profiling the ends of round tubes. Presumably cheaper than a 5-axis mill, but can only be used for doing tubes. But why do you need a 5 axis mill for that anyways? I think it could be done on a cnc lathe...

Also, fun fact: Boeing calculated that, over the life of a commercial jet airliner, saving 1 kg equated to $100,000 in operating cost reductions. Hence why Aerospace is always doing all kinds of expensive shenanigans.

[Greg Locock]

"1 Kg you could get a bonus(higher cost per part ) of around 3€ in 2009 "

Frankly that is peanuts, I can whack out cast iron parts at twice the weight compared with a stamping for that sort of penalty. The reason I say that is that the whole car weighs 1500 kg, so you are only going to pay me 4500 euro to eliminate the mass of the car entirely.


"unless you overspec it so much that you end up with a unacceptably heavy part. "

Yeah, well to be honest real engineers think their way around these things. You are happy enough to risk your life on cast wheels, which see much weirder loads than suspension arms. In the case of a cast arm you could...

a) overdesign it

b) test every one with a force X times that seen in service

c) X ray every part

d)use a high spec material and heat treat it

or some other approach I haven't seen used yet. That being said I'm no great fan of cast steel for suspension arms, I like a lot of ductility in arms.