Investment Casting with Machinable Wax - Prototyping? 3

[Slagathor]

We need to mfg some complex, short run parts in CD4MCu duplex SS. The parts can be machined very accurately on a 5-axis machine using machinable wax. Freeman wax is an oil based wax with no fillers. It can be machined to superfine surface finishes. If can even be polished to a near mirror finish, which would be ideal for our part.

http://www.freemansupply.com/video/products/machwax.htm

Could the wax part simply be sent to a foundry for casting? I imagine not as this wax may not be right for the investment making process.

The other option is to find a foundry specific investment wax, and see how it machines. I recall from handling wax patterns in the past, that foundry waxes for investment casting stainless steels were pretty hard to the touch, but had good lubricity. Seems like they would machine well.

Any experience with using a moldless short run prototyping process like this to produce castings?

 

[MikeHalloran]

Another option is SLA, which can't give quite as nice a surface finish, but can produce delicate and/or impossible- to- machine geometries.

But you should be working with the founder on this, so you can agree on where the vents, gates, and sprues go. In fact, you might make the founder's job easier by including some features for his benefit.






Mike Halloran
Pembroke Pines, FL, USA

 

[Slagathor]

Thanks Mike. Stereolithography has been played with in our industry for years...but it just does not work. Surface finish is critical. Besides...we have the machine tools in house to do what I propose, but not SLA equipment. I guess I need to talk with a the investment casting foundry.

 

[arunmrao]

Selection of waxes for investment casting is not restricted to one type of wax,but often is a blend of waxes,depending on availability,cost and practices in the regions. There are some who specialize in offering wax blends based on the individual requirement. Below 2 links are provided,hope you find them useful in your investigation.

I support Mike's statement the foundry would know best to meet your needs.


UNDERSTANDING INVESTMENT CASTING WAXES - PATTERN-MAKING

http://www.marutiprotectives.com/NCIC.htm

Investment casting institute

http://www.investmentcasting.org/

Learn the rules,so you know how to break them properly.
Dalai Lama

_____________________________________

 

[Slagathor]

Thanks arunmrao,

Those links were helpful. It looks like most of the characteristics of wax that are key to pattern waxes are related to the injection of the wax into the mold itself. It seems that once you form the wax pattern, there is not much else that matters at that point.

I think I may just get some samples some of the non filled pattern waxes with higher melting points, and just see how they machine....

 

[gariartola]

Dear Slagathor,

There is some other facts about the wax besides the injection. Please take into account the following facts prior tp your prototyping:

- Waxes for invest must have low thermal expansion-contraction to avoid primary shell coat cracking/detaching from the surface of the wax model. Even thought your foundry will have a climatized shell room, it is a fact to be taken into account.

- Mirror finish is a nigthmare for the primary shell coats to attach. It is compulsary to micro-etch the wax surface with tricloroethilene, TRISOL or something similar. Go for a material you can etch.

- Shell prime coat grain size will also affect the surface finish. I'm sure your foundry can polish the part after casting.

- Most investment casting waxes are very difficult to machine. You would need to ask for an specialty material to a wax supplier:

http://www.blayson.com

or

http://www.remet.com

- Take into account that the material you choose must not leave any inorganic residues at all after the firing of the mold (low ash content needed) or your will have inclusions in your metal parts.

- The wax you use must be easily attachable to the wax your foundry uses, so that they can build the running, gating and feeding system of the mould with their own wax.

- And last but not least, deffinitely ask your foundrymen; they will asses you in the dimensional correction you have to make in the model to get a metal part in tolerances, the need of ceramic cores, level of acceptable defects, inspection features (LP, X-Ray...) and so on...

Anyhow, I support MikeHalloran with the SLA idea; it goes very well for short runs.

Sorry if I got a bit long and I hope my comments are helpful.

And thanks for the link to the freeman wax, I didn't know of its existence.