Aluminium casting in small runs

Would anyone be able to give a rough idea of costing for a 50mm x 23mm x 11mm part to be die cast in aluminium ?. I am assuming that
die-casting would be the most suitable method though I would be interested to hear pros and cons of other methods.
An image of the part is available at:
http://homepage.ntlworld.com/adrian_harris/t62track.jpg
I've had a few companies quote to CNC mill this part but these have come out at between 150 - 250 for a one off and around 10 each for a quantity of 160.
The longditudinal holes are 4mm in diameter and if these are likely to greatly increase the price I would be happy to drill them out myself.
I have been told this would be suitable for doing myself using RTV molds but that would entail getting kitted out in all the equipment, furnace etc. Mind you, if this isn't viable for casting companies to produce in small runs, I may well delve into setting myself up a casting rig.
Adrian.
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Adrian Harris wrote:

It is a while since I got involved in die casting but tooling will likely be low 10k's. you will still need to drill the longtitudinal holes. Standard casting will need machining all over and drilling plus tooling to hold it. DIY casting? getting set up and learning time will cost you and still need machining. CNC by far the best at the 100 off rate on a commercial basis but if you want the 'fun' and experience of DIY and your time is 'free' then you might just get set up for home casting and save some money.
just my 2p
Bob
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On Mon, 18 May 2009 10:47:54 +0100, Bob Minchin

...or get set up for CNC and mill them yourself from solid...
Regards, Tony
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wrote:

At the price I've been quoted that is actually quite a cost effective answer. I just don't think it should be :-|
Adrian.
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Adrian Harris wrote:
Snip

Just an idea that may mean a bit of casting and a bit of machining The overall piece being 50mm could one not consider either casting or cnc machining it in longer strips then cutting to the correct length?
For example, get it cast or cnc machined in say just over meter lengths and cut 20 out of the bar then drill.
To reduce CNC machining can the dimensions be changed slightly to match standard aluminium bar stock, or can aluminium be stamped, it may just crack.
Lastly and do not know if I missed a section here, does it have to be aluminium could it not be a cast epoxy solution, in which case get one long bar machined as above, use this as a mule, form a mold andwhen set release the bar, use the mold to poor the epoxy into and repeat as many times as you like, cut to length and drill.
Yes you need to allow say an extra 2mm for kerf.
Just ideas.. Adrian
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From experience if you find the right foundry making the master moulds and the first proof part will set you back between 2k to 3k, I use Foundry & Fab in Totnes when required, cannot overstate the importance of using a foundry as they know all about both shrinkage and differential cooling, you don't just want a part to shape and tolerance, you want it strong too. The other thing is they have vast experience in selecting the right alloy for the purpose, this is also hugely significant to the finished product.
Once you have your moulds made per unit prices drop through the floor, and of course a foundry can also do basic finishing machining for you.
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Thanks for the pointers. I'll email them the DXF and see what sort of price they come back with, though it does seem the initial setup costs are the killer.
Adrian.
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Adrian Harris wrote:

How many are you looking for?
If you are only after 1, then a google search for "lost foam casting" will bring up some very good information. Also a google for "gingery charcoal foundry"
Simplest "aluminium casting rig:"
a hole in the ground. a 4" steel pipe about 8" long with a plate welded onto the bottom (your crucible) + some way of picking it up whilst RED hot. A vacuum cleaner on "blow" Barbeque Charcoal. A copy of your part glued up from expanded (white) polystyrene foam with a riser and sprue attached. A (metal!) bucket of builder's sand.
the foam goes into the sand with the sprue and runner showing out the top. put your scrap aluminium in the crucible, put it in the hole. fill the hole with charcoal. light the charcoal and blast with the vacuum cleaner until the aluminium melts.
HOT ALUMINIUM HURTS!
pour the aluminium onto the sprue until the riser fills with aluminium. crossed fingers. wait about 3 hrs to cool
will need machining to final size, depending upon tolerances required.
cost? about a fiver for the charcoal. another fiver for scrap couple of hours work to make the foam pattern
--
bigegg

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Die casting will produce an excellent finish whereas a poly/foam pattern will almost certainly produce a surface finish rough as a bears arse. Somewhere in between will be produced from a conventional wood pattern.
You tooling cost will vary according to what method you go for. A poly pattern will cost pennies, a die for casting may run to 10K or more.
How good do you need the finish to be?
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It doesn't need to be perfect but I'd rather avoid having to machine the parts once they've been cast.
Adrian.
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For a complete set it's 160 units.

Thanks for the pointers.
Another contact has mentioned using Delft Clay casting, which seems relatively cheap, except the mould is a one shot affair so will need rebuilding after each link has been cast.
Adrian.
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If it wasn't for the dimples it would be a snip to CNC. Those raised dimples move it from a 2 1/2D operation to full 3D with associated small moves with small cutters.
If you drilled three holes and welted 3 ball bearing up from the bottom would this do the same end game?
John S.
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The dimples are there to replicate the rivets on the original which hold the two parts together. I hadn't realised (and no-one else has said) that they would increase the level of difficulty in machining the part.
It would be quite easy to replace them with through holes and glue in appropriately sized rivets instead.
Adrian.
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In which case it would be a simple job to have a form cutter made of the largest diameter that can get into the vee of the shape but have the tread radii on the bottom. It may even be possible to mill in one pass either side if the cutter used is large enough to span the widest cut away. Without a drawing it's only conjecture at this point but taking the thru holes as being 4mm it looks to me that it's possible to do the shape in just two cuts.
These could then be milling is strips and cut to length and drilled as required, the fiddly bits done by the user who without being derogatory is working for far less than commercial concerns.
John S.
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Sernd me a dimensioned dng and I will gert you a price for lost wax, the only way to make these in your volume Peter
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I might be all wrong but that looks like a piece of cake for milling freehand with a template, at least for small quantities.
Don Young (USA)
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Hi Adrian
Ok I can't stand it any longer, I have sat here desparately trying to contain myself but have just had to give in .............
What are they? :o)
regards
Dudley
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Seeing as the picture is called T62 track and there are 160 of them it's fair chance they are track links off a tank model.
John S.
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On Tue, 19 May 2009 02:39:20 -0700 (PDT), John S

Correct - 1/6th M4 Sherman to be precise.
Adrian.
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    --Looks like a nice candidate for lost wax casting if those are thru-holes in the end. Maybe you could do a deal with a local college?
--
"Steamboat Ed" Haas : Imagine what I could do if
Hacking the Trailing Edge! : I knew what I was doing...
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