Help with lost wax casting

hi all

im wondering if anyone can help I need to try and replicate this part does anyone know how I can easily make a negative version to the make wax versions for the casting process I've never done any lost wax before but my limited knowledge suggests as this part is too complex to creative a negative simply, I suspect the original was die cast,

its a track link for a model excavator and at €5 from Germany each quite expensive to buy over 100, copyright brigade keep calm 😂

Richard,

I regret that your photos are invisible

Like many before you; you probably need to read **LINK**

http://www.model-engineer.co.uk/forums/postings.asp?th=103028&p=1

MichaelG.

Thanks Michael

I have had many years in the manufacture of wax dies mainly for the aerospace industry and they are fairly simple made of aluminium and as long as you allow for contraction very accurate. You need to talk to the casting company and ask what minimum die size, sprue radius, and casting material contraction. Parts can be cast in stainless steel, aluminium brass etc. If you want any help drop me a message.

David

Hi david

Thanks for taking the time to reply, I want to try and cast them myself the shrinkage isn't to much of a concern to me I want to make a negative of the part without machining a negative mound could I cast the part in something some how then use this ?

Rich

In that case why not get one made in a 3D printer in plastic but if you need 100 parts I cant see how you can cast them yourself. The process is that the wax impression is glued to a runner to allow the metal to be poured in then coated in ceramic paste which is left to dry then a heavy support plaster is applied and dried. many parts are cast at one time depending on the complexity of the item. Then the ceramic is removed by vibration and the parts cut away from the runner system when cool.

David

Richard

As you seem to have parts already to use as a pattern would it be possible to make a mould by encasing one of the parts in a flexible silicone rubber compound and then splitting/cutting this at critical points so that when it is used as a mould it can be released from the wax without causing damage to the wax cast. If possible then several of these wax dies could be attached to a sprue and a multi piece mould made from this. I believe that there are products that you can encase waxes in that harden and can be heated to remove the wax and then used as a mould for metals such as aluminium. The linking pin holes on the tracks would be a problem but they could be drilled later especially if registration marks could be incorporated in the wax mould.

Don't know whether this is a possibility or I am just rambling.

Martin W

PS

Posted slower than Dave  but he confirms the availability and use of a material to encase the wax and used as a casting mould

Edited By Martin W on 18/03/2017 23:56:57

Edited By Martin W on 18/03/2017 23:59:08

Have a look at the video at Investment Castings (congleton) it will give you an Idea as to the of the process. Or contact a local to you casting company, they are usually very helpful.

David

I'd go with RTV silicon as Martin suggests. Make a mould of say 5 links carfully cutting the cured silicon so that the masters can be removed. I've done this a couple of times to make "recasts" Then cut gates and sprues into the silicon.

Pour the wax into the mould and repeat several times until you have suficcient to make a worthwhile metal pour. A soldering iron will melt teh waxes onto a tree which can then either be done in a flask or coated in several layers of investment.

On of your problems will be getting air out as that usually needs a vacuum pump.

Posted by

Richard Cox 18/03/2017 21:52:08
hi all

Im wondering if anyone can help I need to try and replicate this part does anyone know
how I can easily make a negative version to the make wax versions for the casting
process I've never done any lost wax before but my limited knowledge suggests as this
part is too complex to creative a negative simply, I suspect the original was die cast,.

In Mew 208 on page 8 Trevor Ford wrote an interesting article on die-casting aluminium,among
the parts made were track links similar to yours.

Some time ago i wrote some articles for Model engineer showing the lost wax
process and the equipment needed it was published sometime in 1993/4 .
The photo shows the cast wax patterns and moulds and some finished castings.

John

Thanks for the replies lads for example the etc/silicone mold how would I remove the part after would it not damage the mold or if I split the mold to remove part to be copied would it not deform the part when pouring the wax

Rich

Richard.........the whole of the "pattern"is immersed in plaster in a flask with a hole to allow the melt, this is then broken or power jetted to clean up the cast. If multiples are required you immerse your patters in a liquid rubber solution you then have to cut the rubber carefully with a scalpel extract the master and the mould springs back. The pattern has to have an ingate(channel) to allow wax to be injected, thus wax copies are produced which are attached to a central sprue and back to the aforementioned plaster. To complicate matters further the plaster and rubber have to be placed in a vacuum chamber to remove bubbles that might adhere to the original pattern. Mould making can get quite complicated using two half mounds with locating acorns. I am told that good mould cutters, the staff not the knife, are well paid.

The process has been around for thousands ot years originally twirling clay and molten bronze in a centrifugal manner on a rope.

This duplicates what other have written above to show how sophisticated the process is. For a small quantity the caster may be able to include you pattern in a production mould and advise you as the suitability of your patterns

Richard.........forgot to say the hot metal vaporises the wax impression

John

I thought that the mold was heated and the wax drained out and then the residue was burnt out prior to casting. If the wax was left in the mold and then molten metal poured in I suspect the results would be somewhat exciting as the wax vaporised, especially in the confines of a mold.

Martin W

The biggest problem your going to have is with the contraction allowances. You need to find a way of allowing for both contraction in the wax and of the cast part. I would investigate replicating the part with 3D printing first and enlarging it to allow for the above contraction. From memory this is somewhere around 1.5-2%

Martin.......guilty of simplicity..........yes if you are reproducing the calossos of Rhodes, on the suggested part the mould would have an ingate and an "out gate" and the melt would chase the wax out, probably in a centrifuge complying to HSE regs

The model railway cottage industry has this sort of project well covered, using two-piece moulds in high temperature silicone or RTV rubber and casting in type metal or similar material. If you want something more robust as in brass, you'll need to go the lost wax route.

Hi Richard,

I've been reading this thread for the last couple of days with some worrying signs. Could I make a suggestion that if you have a small milling machine and some aluminium plate you could make a tool, the best thing to do is to maybe simplify the design to aid how you make your tool. Even if you have to carry out some machining of the casting when made. You could make the two lungs that stand up parallel and even the bottom of the track flat. If you add a small wedge feed on one end this will help the foundry and make it cheaper, also helps you fettle them clean afterwards. Use a foundry that uses a ceramic shell system not a plaster flask method (Very expensive) The size of your component is small so the foundry should be able to make one tree with 100 plus parts on it. This method will also have the wax autoclaved out then flash fired to remove any residue from inside the tree. The foundry can then pour, cool, cut off and give to you to fettle yourself. If you need any help with your tool design PM me. I spent 20 years as the engineering manager of a large aerospace foundry.

Good luck

Thanks everyone for the replies I have now ordered some two pack silicone rubber to give it a try didn't realise how expensive that stuff is the proper wax isn't cheap either

Rich

Richard........whilst you have had plenty of advice no body has indicated that there are dangers when you start melting metal. Check local and national regs, consider your domestic insurances, safety clothing face and hand protection and the ventilation of toxic fumes. Boring stuff, but there for a reason.