[dbassett74]

I've got an existing part that I would like to make a mold out of so that I can ultimately cast the same part many times. The existing part is a small aluminum intake manifold with a large bore through the middle of it.

Is there such a product that will allow me to simply drop the existing peice in there, have it harden while still be pliable and then remove the mold?

Any pointers on how to accomplish such a thing would be appreciated.

[High Seas]

I've got an existing part that I would like to make a mold out of so that I can ultimately cast the same part many times. The existing part is a small aluminum intake manifold with a large bore through the middle of it.

You didn't mention that the product would be made of - so I take it that a plastic or resin might do it it heat is not too much of a problem.
To make the part many times - You can make silicone or urethane molds fairly easily and there are a number of sites that have intro/starter kits and instructional video/dvds.
I've used these folks for materials they're helpful on the phone and have a pretty good range of product:
http://www.smooth-on.com/howto.htm
Freeman has a wide range of materials for casting and machining:
http://www.freemansupply.com/SampleKits.htm
another is:
http://www.alumilite.com/applications.cfm

Now, if the product is metal, be sure to check out:
foundry 101 and:
http://members.optusnet.com.au/hmbrown/Links.html
and for a generous (long) set of FAQs try:
http://www.ravensforgeminiatures.com/faq20413.html
Metals casting of minatures is a pretty popular hobby, so you may find some forums there that are helpful too.

However, the bore sounds like it will make a simple casting difficult. But there are methods. The simple, Drop-in-and-Cast, is not exactly that easy

Careful, you'll find another hobby!
:cheers: Jim

[ynneb]

It was the large bore through the middle of it that stopped me from answering his question.
I am not sure how that could be done other than making the part in wax and dipping it in ceramic paste and using the lost wax method. This is not a very repedative easy process though.

[HuFlungDung]

Cast metals have a significant shrink factor to consider, so do a lot of casting materials. You'd need to consider if a part that is a few percent smaller than the original would be workable.

[dbassett74]

I would be using aluminum (6061??) as the material. The intake I'm taking about is here:

Picture 1
Picture 2

So would investment (lost wax) casting be the best method to acheive the bore? Would it work something like this:

1) Use some flexible product to make a mold out of this part. Once dried, peel the mold away.

2) Use this mold to produce lost wax molds of the actual part.

3) Place the wax mold inside the sand and make sure the sand completely fills the bore. Then proceed to cast as normal.

I know there would be some machining to be done at the end, but I feel this casting way is a lot cheaper and waists much less material than just CNC machining these parts out of blocks of aluminum...

Any corrections or advice on the above would be appreciated.

BTW, how do you think Ford made this part? Lost wax?? How did they manage to create that large bore? Did they have a plug in the middle and then pulled it out, but I don't see how that's possible with the curve in there and the various protrusions inside.

[High Seas]

I "lifted" this from a parallel thread in Casting Metals, tab down to RPM PROCESS.
http://www.aljcast.com/

[ESjaavik]

Sand cast would be fine. You need a core to make the inside hole. That will be difficult without cutting the original along the parting line to make the core. Then you need to make core prints, that's plugs sticking out of the holes to locate the core. The core must not be too firm or the casting will crack as it shrinks. The core should crush by the shrinking alu.

1 Yes, you could do that. It may even work for making the core without destroying the original. There is a special silicon rubber for this. You need a vacuum stirring machine to use it.

2 No. You cast a polyester model in the silicone rubber, then you

3 place this in the sand.

The tricky part is the core. And the shrinkage that is quite a bit when casting aluminum. You could compensate by adding some putty to the critical places of your original first to make a machining and shrinkage allowance.

Oh, and don't try to cast it in 6061.
Cut up aluminum engine heads are fine raw material for such things.

And beware of the dangers of casting. Wear a full protection! Even slight moisture in a crevice of your raw material may make it explode in your face. How do I know? Well my visor is aluminized to show how! Other than a need for a new set of underwear I was fine thanks to the protection.

[dbassett74]

If not 6061 and not cut up engine heads, then what aluminum do I use? I want this thing to be as high quality as possible so I don't mind purchasing new ingots. What type of aluminum is used for these parts from the manufacturers?

What about lost was or lost foam for something like this? Then I wouldn't need to worry about a core plug, correct? Because the sand would just fill in the empty spaces, right?

[HuFlungDung]

I think Esjaavik is saying "Yes, use old cut up cylinder heads". I've heard the words "high silicon bearing aluminum" in conjunction with sand castings. So if you use a sandcast aluminum for raw material, it should work again for what you want to do.
I found this list of shrinkages of various metals, under the heading "the shrink rule"
http://home.att.net/~philcannon/types.htm

[--colin--]

Parts like this are often investment cast. A wax model of the part is either molded or machined. Sprues and runners are added and then this wax part is dipped repeatedly into a ceramic slurry until a suitable thickness is established. The ceramic mold with the wax inner piece is baked to melt and burn out the wax residue. The final mold is then cast with molten metal. After cooling, the ceramic mold is broken apart leaving the metal casting.

The advantages are not needing to remove the core after the casting operation.

--Colin--

[dbassett74]

Parts like this are often investment cast. A wax model of the part is either molded or machined. Sprues and runners are added and then this wax part is dipped repeatedly into a ceramic slurry until a suitable thickness is established. The ceramic mold with the wax inner piece is baked to melt and burn out the wax residue. The final mold is then cast with molten metal. After cooling, the ceramic mold is broken apart leaving the metal casting.

The advantages are not needing to remove the core after the casting operation.

--Colin--

Interesting process... Everything I have read seems to indicate that the wax (or foam for that matter) is vaporized by the actual pouring of the metal. But your process is a little different. So it can be done both ways? My concern with your process is the ceramic slurry. Seems to be an extra step. Whereas, just burrying the wax or foam into sand and then pouring the metal right in. But I think your process probably produces a better finish. Can you possibly point me to some web sites that sell this wax and ceramic slurry stuff? Thanks!

[--colin--]

Can't help you much with details. I only know from a tour of the Ping golf club manufacturing line in early '80s that they use this investment casting process for stainless steel club heads.

I've seen on the web some folks doing the "lost foam" process that apparently works well by using the hot metal to melt out foam. I imagine that sand if necessary in this application due to the large amount of outgassing that musts be vented. I think that investment casting and die casting are more precise processes that produce fine finishes, whereas sand casting is much rougher, and more common in lower volume and less demanding applications.

The "lost wax" process is common for precicious metal jewelry casting too. they use ceramic slurry and other mold materials, but I'm not familiar with the details. Try looking for jewelry maker supply sources and see what's available. There are lots of custom jewelry makers that product pretty exodic molded shapes. All are small in size but the techniques may be suitable for you. I know from visiting a jewelry supply store they sell lots of waxes and mold making materials as well as many books on the process.

--Colin--

[dbassett74]

Cool, I'll try and find some jewelry supply stores. Hmmm, I wonder if my local Tall Mouse (art/craft store) has this stuff? Seems like the lost wax process is also probably cheaper than foam since I'm guessing the wax can be reused after it's melted out, correct?

[onthemarc]

I think it would work best to make a sand plug for the bore. Then you break out the sand later. It works like this. make a wood plug the shape of the inside bore plus say 1/2 inch longer top and bottom with a taper where it would protrude out the ends, you use this pattern to make a split plaster mold open at the top. use this to ram a core from oil sand. This core fits into your mother mold after you ram the part and remove the origanl part. You need to modify the original part with bondo or the like to have 1/2 tapered nubs at each end so when you ram the part it leaves an cavity at each end to hold the core. you can use your original part to ram your mold but your part will shrink from the original. Did you follow all that

onthemarc

[onthemarc]

You don't reuse the wax it stays in the mold and is vaporized when you pore in the hot metal
onthemarc

[dbassett74]

You don't reuse the wax it stays in the mold and is vaporized when you pore in the hot metal
onthemarc

But colin said that the wax is first melted out before the metal is poured in. So which way is it done? I'm confused now. If it's done colin's way, couldn't the wax be reused? Or is it tost after it's been melted out?

[jgro]

Go check out this page. http://home.iprimus.com.au/cmckeown/patterns.htm Maybe it will explain a little better what onthemarc was trying to explain. You should be able to make that part in a green sand mold with a separate core placed in the mold to make the inside shape. There is no need to go to wax on someting like this.

jgro

[dbassett74]

Go check out this page. http://home.iprimus.com.au/cmckeown/patterns.htm Maybe it will explain a little better what onthemarc was trying to explain. You should be able to make that part in a green sand mold with a separate core placed in the mold to make the inside shape. There is no need to go to wax on someting like this.

jgro

What would the "core" be made out of though? The reason I ask is that the large hole is not straight through and there are protrusions inside which would prevent the core from being able to slide out after casting. That's why I thought lost wax is better for this type of thing.

[jgro]

The core would be made from silica sand and sodium silicate. The two are mixed together and rammed into a mold that is the shape of the inside of the part. Then you blast CO2 through the sand. This will cause a chemical reaction which will harden the sand immediately. After casting the part, the heat from the molten metal will break down the binder in the sand core. You can then go in and break away whats left with a screwdriver or something. It breaks apart easily.

jgro

[cadcam]

Interesting process... Everything I have read seems to indicate that the wax (or foam for that matter) is vaporized by the actual pouring of the metal. But your process is a little different. So it can be done both ways? My concern with your process is the ceramic slurry. Seems to be an extra step. Whereas, just burrying the wax or foam into sand and then pouring the metal right in. But I think your process probably produces a better finish. Can you possibly point me to some web sites that sell this wax and ceramic slurry stuff? Thanks!

Actually the earlier statement was correct in the case of was investment casting.

The wax model is dipped in the slurry and then in most cases added to a tree of many of the same parts.
From here it is heated to help harden the shell at the same time remove the wax.

Now as for this shape and the inner core area.
This part would be done in a two mold config.

First mold would be a soliable mold of the inner core area, this then would be placed in the wax mold and the wax injected around the soliable part in this cavity.

Now the wax part go to basically water but mixed with what I forgot what it was called to male the soliable dissolves and leave you with a wax tool that will be hollow.

I started in the industry as a wax investment tool maker and even worked a a foundry as a tool maker for a few years.

hope this helps.
extra not the basic shrink fator for 6061 in wax with be 1.025