Waterjet cutting (uprights etc) vs casting

[Christopher Catto]

I was wondering if any teams have or plan to use waterjet cutting on thick aluminium alloy plate (25-100mm although more than 50mm would not be used in fsae). I started this thread since I d like to know some opinions. I ve seen the technique mentioned for brake rotors although I normally use laser cutting for steels of up to 5mm.

It has pros that it can be done reasonably fast (faster than wire erosion probably?), repeatably and requires only a 2d drawing like laser cutting. So basically you can draw it one day and have it made the next if you have a good relationship with the supplier.

Cons are that the beam deflects a bit after a certain depth, leaves a bit of a wavy edge, object has constant thickness therefore inefficient in terms of stiffness and overall bulk and obviously the object then needs to be post machined on the cnc like a cast item.

I know some teams like to cast uprights but this seems to me only good in the cost report since setting up a buck, then a mould, then testing it on a car, then refining the design is only a thing that can be done if you keep at it, just like say carbon chassis. Well, my op is that casting is only done by teams with decent resources. Like turbos. Either you have the skill or its gonna bring diminishing returns.

A week ago we had a wooden prototype of an upright waterjet cut (now sitting on our wall as art, how sad...). We ve just done some alum alloy uprigths in 50mm thick stock. Really nice, matl is a bit expensive but relatively ok. Cut is accurate +-0,2 mm. The uprights have a kind of webbed appearance, in order to save weight. Could have saved more but then the extra pockets mean the length of cut would be more than 3,5m so quite expensive. Now all needs doing is shaving a few mm for the bearings to be fitted, then some surfaces machined flat for the wishbone pickup points. Thats all.

Sure, cast would have been cheaper on the long run due to less matl used, could have been lighter and with much more complex shape. But I dont like to have to design and iterate things for a long time since when you factor testing then it can take ages to sign off anything, especially with fatigue life of aluminium and alloys being questionable.

Would like to hear any opinions on this. If you think it sucks or if for FSAE its done by some teams. http://fsae.com/groupee_common/emoticons/icon_confused.gif

[Christopher Catto]

I was wondering if any teams have or plan to use waterjet cutting on thick aluminium alloy plate (25-100mm although more than 50mm would not be used in fsae). I started this thread since I d like to know some opinions. I ve seen the technique mentioned for brake rotors although I normally use laser cutting for steels of up to 5mm.

It has pros that it can be done reasonably fast (faster than wire erosion probably?), repeatably and requires only a 2d drawing like laser cutting. So basically you can draw it one day and have it made the next if you have a good relationship with the supplier.

Cons are that the beam deflects a bit after a certain depth, leaves a bit of a wavy edge, object has constant thickness therefore inefficient in terms of stiffness and overall bulk and obviously the object then needs to be post machined on the cnc like a cast item.

I know some teams like to cast uprights but this seems to me only good in the cost report since setting up a buck, then a mould, then testing it on a car, then refining the design is only a thing that can be done if you keep at it, just like say carbon chassis. Well, my op is that casting is only done by teams with decent resources. Like turbos. Either you have the skill or its gonna bring diminishing returns.

A week ago we had a wooden prototype of an upright waterjet cut (now sitting on our wall as art, how sad...). We ve just done some alum alloy uprigths in 50mm thick stock. Really nice, matl is a bit expensive but relatively ok. Cut is accurate +-0,2 mm. The uprights have a kind of webbed appearance, in order to save weight. Could have saved more but then the extra pockets mean the length of cut would be more than 3,5m so quite expensive. Now all needs doing is shaving a few mm for the bearings to be fitted, then some surfaces machined flat for the wishbone pickup points. Thats all.

Sure, cast would have been cheaper on the long run due to less matl used, could have been lighter and with much more complex shape. But I dont like to have to design and iterate things for a long time since when you factor testing then it can take ages to sign off anything, especially with fatigue life of aluminium and alloys being questionable.

Would like to hear any opinions on this. If you think it sucks or if for FSAE its done by some teams. http://fsae.com/groupee_common/emoticons/icon_confused.gif

[drivetrainUW-Platt]

I think you should just run the wooden one on the car for competition http://fsae.com/groupee_common/emoticons/icon_cool.gif

I think most people CNC machine there aluminum uprights, but I could be wrong.

[Grant Mahler]

I would agree with you in nearly everything you said.

We have and use a waterjet - an old Flow BENGAL. There are newer and better machines, but it works for us.

The new machines can do blind cuts or pockets or whatever you want, 3, 4 or 5 axis, 2D/3D, whatever.

Our machine uses a LOT of sand, the cuts are imperfect at best, and with stock material 100mm thick there will be at least ~0.040" draft between the cut/uncut sides. There will be waves, as you described. There will be surface "clouding" where the cuts are started if you have any cuts that cant leadin/leadout with enough space.

We use our waterjet for an awful lot, and we cnc'd our uprights. I would be wary of any uprights that were entirely waterjetted - you need CNC to clean up the parts.

[BenB]

Are there seriously teams who cast uprights? What type of casting do they do and how much is set-up cost for that?

[Coombesy]

Sounds damn cool, and not too expensive. Do you have a pic you could post?

[Brian Barnhill]

We actually have a casting facility/casting research lab on campus (in the same building as out shop space actually) We will be casting aluminum - our foundry has done magnesium in the past, but they wouldn't do the setup for our team for a limited run.

Right now, we aren't considering casting the uprights, but we are considering a few other parts. We are also getting a new Hass VM2 in 2 weeks, which will make machining our molds much easier.

In our case we will be casting multiple copies of parts to eliminate manufacturing time for identical parts. It will also allow us to machine some more complicated shapes without worrying about fixturing, which was a bit of an issue for us in the past.

[flo]

We have sand cast uprights on our curent car.

front upright (http://www.lionsracing.de/component/option,com_ponygallery/Itemid,32/func,viewcategory/catid,56/lang,de/)

rear upright (http://www.lionsracing.de/component/option,com_ponygallery/Itemid,32/func,viewcategory/catid,57/lang,de/)

The sand cast uprights cost much more than cnc parts. The molds are expensive to print and after casting you have to cut the bearing carriers out.
The cast uprights gave us the facility to realize a complex suspension geometrie. Instead of milling our uprights we used the resource to mill our wheel shafts.

florian

[Biggy72]

Pittsburg State University last year at West had investment cast uprights. Not pretty, but they said they did pretty well in the design and cost events. But I can't seem to find any pictures of their uprights...

[TG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BenB:
Are there seriously teams who cast uprights? What type of casting do they do and how much is set-up cost for that? </div></BLOCKQUOTE>

Ben,

A lot of art departments at schools have the ability to do castings. If you check with them, you might find that they have a small foundry to do lost wax castings or some other form of casting.

[Christopher Catto]

Florian. I cannot seem to get the link to work.

Does anyone have a total costing for cast uprights (first buck, first mould, material volume hence cost, post-machining)?? Someone from ETS or some of the german teams?

For the waterjet cut examples I made at work, the total cost before machining comes to around USD 380 each. But this is for the first 6 we make and the material is very thick since it goes on a production car and we cant afford anyone to get hurt. We have a big plate 1m x 1m and we will use the offcuts for other stuff. The machining is not more than say 75-100 bucks since it is very simple orthogonal stuff to make some faces true. The waterjet leaves a wavy surface but its still pretty damn accurate, i measured max 0,3mm difference from one side to the other meaning you can leave just 1mm extra for machining. Just the corners need a decent radius of 3mm to avoid the beam overshooting or wandering.

Cant remember the alloy spec but its somthing like AlMg4.5Mn which is roughly like SAE5083 and we could have used a more expensive version with copper alloying also which would be close to 6061 or 7075.

Unfortunately my employer does not allow me to post pics so the the uprights will only be visible if or when pics are uploaded in this site http://www.k1roadster.nl/concept/foto.php

I reckon for casting, the cnc machined buck with 3-4deg draft angles would cost in the region of USD 1000. Then if you go cheap you can cast in sand or pressure cast in steel. I would have gone for steel but again the mould is expensive to machine.
My problem was not the cost of the stuff, just the uncertainty if I need to make a change, since the last week or so I was adjusting details in order to engineer the damper mount. I cant think for FSAE it is a benefit to cast rather than machine unless one can high pressure cast one of the good alloys. In that case you save material but for say 2 uprights plus 2 spare i cant believe the cost is much better than just buying a thick block of 6061. In fact, with Titanium sheet, you can make pretty much any uprights you want, and I reckon for less price. Only bummer with Ti is the waiting time to receive it unless you are a uni that has a lot of material flow for other projects...

[Brian Evans]

Oh for the good old days... My dad was a die maker when he was 17 - he made casting dies (the positive from which a negative mold is formed) out of mahogany with normal wood working tools - circa 1946. My 1972 sports racer has cast aluminium front and rear uprights (and pedals and various other bits) made with hardwood bucks and cast in the backyard. By, coincidentally, Jim Leach - on the staff of University of Illinois!

fun and profitable too! They actually sold their cars to people.

Brian

[Christopher Catto]

i know a person who would have done the die in wood. unfortunately i did not trust that it would be very easy to make the shape i designed due to the nature of the ribs and features. Had it been a different shape I would have given it a shot. I thought it was a bit of a waste of energy to make a lovely wooden die only to then realise that something small needs changing and that you cant reach the detail because of the shape. still, casting will be looked at in future. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[flo]

Hi Christopher

The links should direkt you to our image gallery. The images enlarge in a pop-up window. I can`t find anything going wrong.

The cast including heat threadment and radiography should cost about 180€. I haven't any numbers about the mould and post-machining.

Instead of wood i may choose a rapid-prototyping method especially when the shape is complex.

[Christopher Catto]

Flo
ctrl clicking seemed to solve my prob or maybe your site was slow the past days and my ie was playing tricks on me. now i see the design and it is very nice.


do you have any links to papers or info that helped you with making the upright hollow inside? i know wax can be used and also other materials but am wondering if there is any site or pdf with a lot of photographic evidence on casting of hollow parts (I guess all sculptures are hollow so I will look at what info I can find). Your upright looks like it has a very good finish so I would say it has had a lot of effort with regards to the technology used, hence why I am interested in any patented technologies or companies that specialize in this kind of stuff (but I know, you guys did it yourselves.)

I have seen some 80s formula cars (also hillclimb cars) and some ran hollow uprights but the finish was that of a sand casting and I have seen them damaged examples (also seen a cracked Murcielago rear upright due to crash damage). Having seen the inside I was not too impressed about the finish of the component especially when it comes to porosity, grain structure, imperfections which are similar to stress raisers. I think pressure casting in a stiff (steel) mould would be ideal, more expensive but worth it I would say.

[flavorPacket]

sand casting an upright is a really bad idea in my opinion for the exact reasons you give, Chris: Poor dimensional control, porosity issues, absolutely no grain structure control, etc.

If you must cast an upright, at least use investment casting.

[jdstuff]

If you have access to a good machine, water-jetting can produce some nice parts. Thickness isn't too much of an issue....I know that I saw the machine we had access to make some damn nice parts out of 10" thick Al!

When I was in FSAE, we probably got the most use out of our waterjet machine by simply doing profile cuts, and then finish machining on a mill (for larger parts such as belcranks, uprights, etc). It saved a bit of time and a LOT of material, seeing as how we could nest the part profiles quite nicely. We were able to work a lot of savings into the cost report this way as well....
http://shim1.shutterfly.com/procgserv/47b7ce32b3127cce98548b679b5700000027100AaMWLJw3at2 Og
http://shim1.shutterfly.com/procgserv/47b7ce32b3127cce98548b799b4900000027100AaMWLJw3at2 Og

[CU - Andrew]

At the 2007 competition, the judges commended us for our simple 2D upright designs. We plan to waterjet cut them this year for time and cost report considerations.

[overdrive535]

The car we built for last year but did not compete with has flow jet cut front uprights (you don't want to know about the rear setup). We had them done locally and they turned out really well. There was a decent bit of machining left to be done after we got them back, but all in all it went well. Talking to him, it seems that the thickness of the material and cut time are related (duh!), but if you're around 1.5 - 2 inches and want them cut quick, expect some oddities. If done correctly, they can be machined off. I'll see if I can find some pictures of them to post.