Casting AL7075 and AL6063

[Kasrawy]

Hey all, we are a first year team from Egypt and we were thinking of manufacturing our hubs, rotors and uprights from AL7075. The problem is that the raw materials available here are in billet form only and are not large enough for machining the upright and rotor out of, this left casting as the only viable option for us.

Now we have it on a semi-reliable source that AL70XX and 60XX series are not fit for casting (due to low fluidity when molten). I am looking for confirmation on that fact and to ask whether the fatigue loading in aluminum hub would cause any problems for a casted part (whether the grain deformations due to casting would lower the endurance limit for example).

Also one last thing: does running a fixed steel front spindle that goes through the upright cause any problems based on your experience. we have the spindle fixed to the upright using a flange fitted with 5 M8 bolts, the spindle has a protrusion that goes through the upright in a transition fit that is mostly there for alignment.

Thanks in advance

[Kasrawy]

Hey all, we are a first year team from Egypt and we were thinking of manufacturing our hubs, rotors and uprights from AL7075. The problem is that the raw materials available here are in billet form only and are not large enough for machining the upright and rotor out of, this left casting as the only viable option for us.

Now we have it on a semi-reliable source that AL70XX and 60XX series are not fit for casting (due to low fluidity when molten). I am looking for confirmation on that fact and to ask whether the fatigue loading in aluminum hub would cause any problems for a casted part (whether the grain deformations due to casting would lower the endurance limit for example).

Also one last thing: does running a fixed steel front spindle that goes through the upright cause any problems based on your experience. we have the spindle fixed to the upright using a flange fitted with 5 M8 bolts, the spindle has a protrusion that goes through the upright in a transition fit that is mostly there for alignment.

Thanks in advance

[shark.ashwa]

Have you thought of importing the material from outside?? http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif
Or you could just use welded steel uprights!! Have seen some beautiful ones on these forums.. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Sharath

[Jon Burford]

Agree with welded steel, Ours are under 500g this year.
Although we are using 7XXX for our wheel hubs.

[Kasrawy]

we are exploring all options, but the question remains: can 7075 alloys be melted down and cast?

[shark.ashwa]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kasrawy:
we are exploring all options, but the question remains: can 7075 alloys be melted down and cast? </div></BLOCKQUOTE>

No, I don't think so. In the time I spent looking for hollow cast uprights for our car, I came to know that Al 30XX is a good alloy for casting. You might want to look into that....

Sharath

[Zac]

Google says it isn't a good idea, as 7075 relies on a very specific tempering process.

I would recommend either importing material blanks that are in the proper size, changing your material, looking at a sheet metal upright, or using ATV parts.

Whenever I see the words "first year team" coupled with things like cast parts or overly ambitious chassis controls I cringe a bit. Focus on getting stuff done, not being fancy.

Also, cast 7075 rotors sounds like a terrible over-complication of one of the simplest parts on a car.

[Kirk Feldkamp]

A356-T6 is a fairly common cast replacement for 6061 in my experience. Is has less tensile and yield strength you ask? Yes, but it generally ends up thicker because of realistic minimum casting thicknesses. There are other alloys like 771-T6 that would be almost exactly the same strength properties. Check out http://en.wikipedia.org/wiki/Aluminium_alloy to start your search for more information. Matweb.com is also a *fantastic* resource for materials information.

I find it sorta comical that teams in some areas of the world are quick to use the excuse that certain material sizes and/or car parts are "unavailable", and this is often attributed to it being "their country." Do you guys really think anyone anywhere a one-stop shopping experience for stuff like this? No way! There are all sorts of sizes and materials that can't be found without some *serious* searching. I once spent 3 days calling dozens of places in North America trying to find enough 2.75"x0.035 321 stainless tubing to do a new vehicle's exhaust. I found ONE place on the other side of the country, and if you asked all of the other shops I talked to before that, they would say it didn't exist! In that case, it was the only size, thickness, and alloy that would work reasonably given the project requirements... so I had to find a way to make it happen. If you don't want to run into these sorts of problems in the future, it is best to learn how to design to stock sizes!!! This true now for this project, and will continue to be true when you start working.

It also sounds like you guys might benefit from learning how to design for manufacturing!!! Just because you can actually design and build something doesn't mean it's a good idea. If I'm understanding what you're asking... you're talking about a live spindle with a transition fit that bolts onto the upright?! There are usually easier to manufacture (and potentially lighter) ways to go about this. How did the designer of these parts settle on that concept?

I agree with Zac. If this is where you guys are at (asking these questions), it's probably best to get some more experience with machined parts first before trying to tackle cast parts.

[Kasrawy]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kirk Feldkamp:

I once spent 3 days calling dozens of places in North America trying to find enough 2.75"x0.035 321 stainless tubing to do a new vehicle's exhaust. </div></BLOCKQUOTE>

I know you are trying to be helpful and I do appreciate the advice but if you were here you would better understand the situation. If you spent 3 days searching for tubes we've been at it for more than a month and most suppliers don't even comprehend what we are asking of them let alone tell us that it doesn't exist so please try not to asses our situation so brazenly before seeing it from our standpoint. But thanks for the advice nonetheless.

[Simon Dingle]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kirk Feldkamp:
A356-T6 is a fairly common cast replacement for 6061 in my experience. Is has less tensile and yield strength you ask? Yes, but it generally ends up thicker because of realistic minimum casting thicknesses. </div></BLOCKQUOTE>

Also, it still has the same modulus of elasticity and the vast majority of FSAE components (especially suspension components) are stiffness limited long before they are yeild stress limited. 7075 is just unnecessary in most applications.

[Seeger]

If I recall properly from when Rolling Camel posted a lot previously. That it was either a university or government issue with importing things into Egypt, something about they cannot buy anything outside of the country unless it does not exist in Egypt.

[Zac]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kasrawy:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kirk Feldkamp:

I once spent 3 days calling dozens of places in North America trying to find enough 2.75"x0.035 321 stainless tubing to do a new vehicle's exhaust. </div></BLOCKQUOTE>

I know you are trying to be helpful and I do appreciate the advice but if you were here you would better understand the situation. If you spent 3 days searching for tubes we've been at it for more than a month and most suppliers don't even comprehend what we are asking of them let alone tell us that it doesn't exist so please try not to asses our situation so brazenly before seeing it from our standpoint. But thanks for the advice nonetheless. </div></BLOCKQUOTE>

Welcome to the real world. If the material doesn't exist in the stock size you'll need to either pick a different material or pick a different part design. In general a cast part is a lot more work than a machined part.

[Kirk Feldkamp]

That was my point, but it was apparently lost in the red mist. The process I tend to take is to figure out what's available before I start designing anything... and then tailoring my design to that. If all else fails, then you can also figure out a differnt process (such as casting). In the case of casting, the design goes well beyond the part at hand, which is why I don't recommend it for a new(er) team or designer. The tools, mold(s), mold material(s), casting process, gating, any core(s), runner(s), parting lines, casting flash, etc. all factor in to how you design a part. Porosity, inclusions, material composition, grain structure, casting-to-machining features and datum structure... these are all complications that you'll have to deal with if you do a casting. Generally, the resources required to proper castings are only justifiable if you're doing moderate quantities. There are some cool processes, like rapid protyping of a wax or plastic pattern for investment casting, that make sense for very small quantity runs... but they too have their quirks and aren't usually cheap. If you can't find billets in the size/material you want, I doubt you're going to find any local vendors that do that kind of work anyhow.

[Adambomb]

As a general rule, 4-digit Al alloys are "not for casting," and 3-digit Al alloys are for casting.

I would use mild steel sheet before I attempted to cast 7075, even if I had decent casting facilities. As Kirk mentioned there are just wayyy too many things to go wrong, even after the very large amount of work required to get a good set of molds, etc.

I'm not sure if cast 7075 rotors were a serious suggestion, but there are WAYYY too many things wrong with that idea for me to elaborate!