Sand casting

[Sphinx]

Hi everyone, I'm hoping some of you might be able to guide me in the right direction here.

How would I go about getting a car component; in this case a plastic thermostat housing, cast in aluminium?
Is it a simple case of making a mould from the original (in what?) and then casting it in alloy?
In case you couldn't tell, I really don't know the first thing about this

It's not something I'm going to attempt in the shed but I'm considering approaching people to get things made.
For a part like this that won't need much/if any machining, is a simple process or am I way off the mark?

Thanks

 

[mike os]

probably easier to have one machined I would think

 

[Luke]

Yes, a cast part will need machining anyway.

Cast surfaces wont be suitable for sealing to other surfaces or connecting pipe, for example.

 

[the artfull-codger]

hmmn, it all depends on the shape & cross section of it, there's a number of issues to this, I guess if it's plastic it will probably have been injection moulded under pressure so possibly have thin sections,if you sand cast it, the thin sections will possibly not run as it relies on gravity,even with a large runner also it will be slightly smaller due to shrinkage as most[not all] metals shrink on cooling,if you know anyone with a ''backyard'' foundry they might give it a go for you.

slan go fol

 

[astro_al]

Best thing is to find a foundry that does ali and then ask them what type of pattern they want.

The best one near you was G F James, until they went into receivership about a year or so ago. Been there for decades - one bad contract finished them off (as I understand it).

You also need to allow for shrinkage of the casting, so for example, you cant just copy a part and have it come out the same size. Typically around 10% smaller for ali after casting I think.

Generally, you'd need to machine / polish / fettle / fart about with the part after casting anyway, so unless its very complex or you want loads of them, just machine it from scratch.

Cheers, Al.

 

[astro_al]

Sorry artful - synchronous posting!

Al

 

[drjim]

Someone posted a link to this recently...

http://forums.vwvortex.com/showthread.php?4662626-The-complete-guide-on-casting-parts

Should give you an idea of what is needed.

 

[the artfull-codger]

no probs astro, we were probably typing away at the same time!!!

slan go fol

 

[mike os]

for a simple part I can talk you through the whole process...something I am looking into as a hobby.... but not worth the time to make the pattern, cores, mould, then cast & machine..... unless it is a form almost impossible to machine I would forget casting.

 

[hareng]

Lost wax method?

Would still need machining though.

 

[mike os]

Lost wax method?

Would still need machining though.

and have to make the core/template

 

[Drains]

What car Sphinx?

 

[Robotstar5]

You also need to allow for shrinkage of the casting, so for example, you cant just copy a part and have it come out the same size. Typically around 10% smaller for ali after casting I think.

The pattern shop at the foundry I worked had rules calibrated in "inches" to accomodate the shrinkage for the type of metal being cast. Handy for fishermen too I suppose!

 

[smarty]

You can get greater precision with lost wax but trouble is you get more shrinkage since the wax shrinks as well as the metal!

Also aluminium is a pain to cast unless its a certain alloy and this might be the wrong alloy for the intended purpose. I've cast things using alloy wheels from the scrappy before and the secret is in the degassing (since it just won't run due to the rapid oxidisation of the metal and the gasses absorbed from the propane combustion). A little chunk of loo blue does the trick!

Whatever way you look at it machining is probably the way to go. Melting stuff is more fun though!

 

[Sphinx]

Wow! Thanks guys! Lots of replies

The item is the new BMW Mini thermostat housing as it's a known weak plastic part that warps and cracks very easily.
I've heard of them being a serious problem and my own experience with BMW's (older 3 series) is that items re-cast in alloy sell well, so it was an idea I wanted to explore.

 

[brightspark]

Wow! Thanks guys! Lots of replies

The item is the new BMW Mini thermostat housing as it's a known weak plastic part that warps and cracks very easily.
I've heard of them being a serious problem and my own experience with BMW's (older 3 series) is that items re-cast in alloy sell well, so it was an idea I wanted to explore.

theres your chance get it patented and get em made in china

 

[Andy from Workshopshed]

I've cast things using alloy wheels from the scrappy before and the secret is in the degassing (since it just won't run due to the rapid oxidisation of the metal and the gasses absorbed from the propane combustion). A little chunk of loo blue does the trick!

Using something like wheels is a good source material, you'll have a terrible time if you try to use cans... My first casting was some old strip (the type that hold down carpets). Since then I've used old hard disk shells which work very well. I've not needed to degass but I do use charcoal rather than propane as a fuel.

Looking at some pictures of "Thermostat housings" on google, that's a very advanced shape to produce. It would need both patterns and cores and the thin walls might be a problem. You might be better producing a block roughtly the right shape then machine the holes etc.

 

[Sphinx]

Thanks again for the replies guys.
My e36 bmw had a plastic housing which is a common failure, you can buy cast alloy ones from the states as an upgrade (which I did) and it's an exact copy of the plastic item, just in alloy lol I thought the same could be done for the Mini item; it's a little more complex, but not by much. It was just an idea to be honest, when I have more time and money I'll look into it.

 

[Justme]

Can you not use a flat plate with suitable fixing holes & a pipe stub welded on?

Then fit an inline stat in the hose.