How to copy existing part to make a mold?

[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]

Originally Posted by 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.

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!
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]

Originally Posted by --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--

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--