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John Stevenson
05-21-2012, 05:43 PM
Be sure to read to the end.

http://www.homemodelenginemachinist.com/index.php?topic=18727.0

Weston Bye
05-21-2012, 06:25 PM
I saw this done in research back in the mid- '70s by Chevrolet. They did it differently though in that they glued slabs of closed cell styrofoam together to form cylinder heads. Four were glued to foam gates, vents and risers to form a "tree". The tree was then dipped several times into a ceramic slurry much like pottery glaze. Once dry, they fluidized a barrel of dry sand with compressed air from the bottom and dipped the tree into the sand. Next, they vibrated the barrel to settle the sand firmly around the part and into the internal passageways. Then, bypassing the usual burnout step as used with lost wax, they poured the molten aluminum in, vaporizing the foam in the process. (seems like this could lead to some porosity issues) I don't know if the process was perfected or is now being used, but I do remember seeing some aluminum heads with a curious surface texture that resembled that of a styrofoam coffee cup.

DICKEYBIRD
05-21-2012, 06:34 PM
Very clever fellow who obviously has the CAD modelling process well in hand.:eek:

It was uncomfortable to read how some on the forum responded to the young man's posts. "Go build a wobbler first." Yeah, right.:rolleyes:

George Bulliss
05-21-2012, 06:44 PM
Very interesting thread. The guy sure has talent, but I think he has even more patience, both for building up the many layers of the pattern and for sticking with the thread. He may be doing his first scale engine, but I'm guessing by the looks of that pattern that he has done this kind of thing a few times before. Thanks for sharing.

George

lazlo
05-21-2012, 06:59 PM
Very interesting thread. The guy sure has talent, but I think he has even more patience, both for building up the many layers of the pattern

He's doing manual 3D printing :)

G1K
05-21-2012, 07:00 PM
I saw this done in research back in the mid- '70s by Chevrolet. They did it differently though in that they glued slabs of closed cell styrofoam together to form cylinder heads. Four were glued to foam gates, vents and risers to form a "tree". The tree was then dipped several times into a ceramic slurry much like pottery glaze. Once dry, they fluidized a barrel of dry sand with compressed air from the bottom and dipped the tree into the sand. Next, they vibrated the barrel to settle the sand firmly around the part and into the internal passageways. Then, bypassing the usual burnout step as used with lost wax, they poured the molten aluminum in, vaporizing the foam in the process. (seems like this could lead to some porosity issues) I don't know if the process was perfected or is now being used, but I do remember seeing some aluminum heads with a curious surface texture that resembled that of a styrofoam coffee cup.

Yes, it is - or at least very similar. Here are two photos of a 16V 4 cylinder head for a GM engine.

http://i531.photobucket.com/albums/dd358/gonekayatgmailcom/head01-1.jpg
http://i531.photobucket.com/albums/dd358/gonekayatgmailcom/head02.jpg

Ryan

John Stevenson
05-21-2012, 07:19 PM
I now have an excuse for buying a laser cutter :D

lazlo
05-21-2012, 07:21 PM
I now have an excuse for buying a laser cutter :D

You're too old to have that kind of patience John. Get Young Son to punch out and glue all the pieces together ;)

John Stevenson
05-21-2012, 07:39 PM
I don't need the patience, I just need the excuse........:rolleyes:

oxford
05-21-2012, 10:01 PM
I saw this done in research back in the mid- '70s by Chevrolet. They did it differently though in that they glued slabs of closed cell styrofoam together to form cylinder heads. Four were glued to foam gates, vents and risers to form a "tree". The tree was then dipped several times into a ceramic slurry much like pottery glaze. Once dry, they fluidized a barrel of dry sand with compressed air from the bottom and dipped the tree into the sand. Next, they vibrated the barrel to settle the sand firmly around the part and into the internal passageways. Then, bypassing the usual burnout step as used with lost wax, they poured the molten aluminum in, vaporizing the foam in the process. (seems like this could lead to some porosity issues) I don't know if the process was perfected or is now being used, but I do remember seeing some aluminum heads with a curious surface texture that resembled that of a styrofoam coffee cup.

I always heard this method refered to as lost foam casting. GM may still be using it. Last I personaly have seen it used was in the original Saturn S series blocks and heads of 1991-2002. Unfortunaly when I took the tour of the Saturn plant they were not producing these motors anymore. Some of the earlier techs got to see the foundry when on the plant tour and see the process. I have seen some of the styrofoam molds of the motors though.

J Tiers
05-21-2012, 10:41 PM
Laser cutters are the cat's whiskers......

We just had some gears cut out of a plastic material in order to make a simulator for a client's system. The new guy has a friend who built a cnc laser cutter while at school in Rolla MO at Missouri S&T.

They really turned out nicely. It's a strange plastic, looks clear, but edgewise it is a deep blue.

The simulator is for the mechanical system of a servo which has two encoders that we read. So we had the laser cutter guy make us a smaller scale version of the entire gearing system and support parts out of 1/4" thick plastic so we can use it for development. Sure went faster than machining the gears, considering that one has something like 100 teeth.....

he has also cut us gaskets, insulator pieces, etc, etc.

Oh, yeah.... That "styrofoam" engine part is flat out crazy-looking....

Circlip
05-22-2012, 03:09 AM
Hope the "Lad" mentioned in the O/P isn't put off by the patronisers. Only problem he might have had with melting the wax out of the sand (?) has been covered.

Without starting a flame war, Water jet cutting is far more versatile, but yes, a cheap W/J is not on the market - - - yet.

Regards Ian.

oldtiffie
05-22-2012, 03:35 AM
That is very nice creative well planned and executed work.

If I had laser or water-jet cutting job to do, I'd "farm it out" to a specialist.

I am very aware of my limitations in many ways and am continually up-dating the list - which is not small.

Weston Bye
05-22-2012, 04:09 AM
I always heard this method refered to as lost foam casting. GM may still be using it. Last I personaly have seen it used was in the original Saturn S series blocks and heads of 1991-2002. Unfortunaly when I took the tour of the Saturn plant they were not producing these motors anymore. Some of the earlier techs got to see the foundry when on the plant tour and see the process. I have seen some of the styrofoam molds of the motors though.

My involvement was as a controls designer with a machine tool builder who built some of the research equipment for preparing the materials and molds for casting as described in my previous post. Yes, the process was indeed called lost foam casting.

I'm hoping to do some home shop (back yard) experiments with lost foam casting this summer when (if) I get my melting furnace finished.

I will throw an idea out here: Too cheap for a laser CNC? Build a CNC-guided nichrome hot wire foam board cutter - like a wire EDM. Nothing new, they are out there. Google: CNC foam board cutter.

vpt
05-22-2012, 08:12 AM
Yes, it is - or at least very similar. Here are two photos of a 16V 4 cylinder head for a GM engine.

http://i531.photobucket.com/albums/dd358/gonekayatgmailcom/head01-1.jpg
http://i531.photobucket.com/albums/dd358/gonekayatgmailcom/head02.jpg

Ryan



I hate that stuff! Weak, and near impossible to weld.

aboard_epsilon
05-22-2012, 08:22 AM
I hate that stuff! Weak, and near impossible to weld.

what is it ..compressed aluminium balls ?

if so ..seems that it would become porous like an aqurium air stone

all the best.markj

TGTool
05-22-2012, 10:30 AM
Jewelry making suppliers have wax in various hardnesses and forms including sheets. I would think the guy in the link might be ahead by laser cutting wax sheets and stacking them cutting out the silicone mold step. He could then do plaster casting and burn out the wax and he'd be ready to cast.

lazlo
05-22-2012, 11:27 AM
I hate that stuff! Weak, and near impossible to weld.

Are you being sarcastic Andy? That's just standard lost-foam aluminum casting.

Yes, it's a bitch to weld, but the strength is as good as any aluminum casting?

Spin Doctor
05-22-2012, 07:39 PM
IIRC the original rapid prototypers used paper about .005 think. About the same as 24LB copy paper. It really is a clever way to go about it

sansbury
05-22-2012, 08:32 PM
Jewelry making suppliers have wax in various hardnesses and forms including sheets. I would think the guy in the link might be ahead by laser cutting wax sheets and stacking them cutting out the silicone mold step. He could then do plaster casting and burn out the wax and he'd be ready to cast.

Yes, but if his first wax cast fails, the silicone mold makes it easy to make a second wax core.

vpt
05-23-2012, 09:08 AM
Are you being sarcastic Andy? That's just standard lost-foam aluminum casting.

Yes, it's a bitch to weld, but the strength is as good as any aluminum casting?


I notice on protruding tabs, bolt holes, and smaller "things" that there will be more porosity and it seams I see more broken off stuff with these castings than others. I know the styrofoam "look" doesn't go very deep but it goes plenty deep enough to be impossible to get perfectly clean for a TIG weld. These castings will have more voids and cavities than other "normal?" castings.

The last thing I saw with this kind of casting is OMC outboard motors. The head I used on my 60hp rebuild had visible voids, craters, and weird spots even right in the combustion chamber. There were places in the water jackets that had holes where they shouldn't be and casting where there should have been holes.

I don't know what this guy did to this head but you can see the porosity of this OMC head.

http://zetal.com/boats/84trophy/101_3764.JPG

wierdscience
05-23-2012, 09:30 AM
Absolutely no reason it won't work,he could also fill the steps with polyester filler and sand off smooth.If he has the % oversize right,the draft angles will all be the same.Some filling,some sanding followed by some lacquer and he will have patterns.

wierdscience
05-23-2012, 09:36 AM
I notice on protruding tabs, bolt holes, and smaller "things" that there will be more porosity and it seams I see more broken off stuff with these castings than others. I know the styrofoam "look" doesn't go very deep but it goes plenty deep enough to be impossible to get perfectly clean for a TIG weld. These castings will have more voids and cavities than other "normal?" castings.


Your right,lost foam has it's trade offs,mainly the combustion products of the foam ending up in the alloy.

IIRC this was first developed by Mercruiser and later adopted by GM Central foundry to produce Corvette blocks.

TRX
05-24-2012, 04:53 AM
The first mass production use of lost foam casting was (at least according to Ford's propaganda department) the cylinder head on the Ford Escort CVH engine.

Weston Bye
05-24-2012, 07:41 AM
From Wikipedia:

http://en.wikipedia.org/wiki/Lost-foam_casting


Lost-foam casting was invented in 1964 by M.C. Flemmings. Public recognition of the benefits of LFC was made by General Motors in the mid 1980s when it announced its new car line, Saturn, would utilize LFC for production of all engine blocks, cylinder heads, crankshafts, differential carriers, and transmission cases.

Not to say that the two preceeding posts are incorrect, as everything from Wikipedia must be considered suspect until corroborated.

michigan doug
05-24-2012, 05:41 PM
I have experimented a few times with lost foam casting. One advantage is that you use plain sand, not green sand, not petrobond, but plain sand. Use it over and over.

I cast a 9" pulley with cast lightning holes. Then I cast a separate bushing to mount it on my generator. I machined in grooves to accept a 6 rib serpentine belt.

Turned out great.

Make sure your aluminum is properly hot, I had two incomplete fills before I got a good casting. And pour as fast as you SAFELY can.

Pretty stinky.

I used the high density foam, not that stuff made of low density bead stuck together to make a sheet.


Finest regards,

doug