investment casting shrinkage

[Surface]

I am in the process of machining a pattern for an

investment casting. This pattern will be used to create a silicone mold. Then wax will be poured into the silicone mold. When melted, the wax pattern will create a void in a ceramic type material and molten brass will be poured in its place.

Pretty common investment process.

 

Question is, how much shrinkage is likely to occur?

The foundry I am going to is sort of a Mickey Mouse outfit, but beggars can't be choosers. They recommend making the pattern 8% larger for shrinkage. This sounds like an awful lot. Has anyone had any experience in this type of stuff?

[cadcam]

I follow more of a scale for wax in most cases of 1.025.

 

Scott bond your thought?

[Scott Reiner]

I remember it being 1.025" shrink, however it was for a finished iron cast, not a brass finished cast. Best option is to take a "very near" and measure one of their moulds and a cast from it to work out the shrink. Two foundaries will give you different castings based on their process controls.

 

HTH

 

Scott

[BernieT]

1.025 (2.5% shrink) is common for hard tooling for investment casting of steel parts. 1.015 (1.5% shrink) for aluminum, again hard tooling. These shrink factors are determined by the foundry.

 

For as many steps as you're going thru 8% seems reasonable.

 

Every foundry has their own shrink requirements and they learned it by experience.

 

My suggestion would be to use their recommendation AND if possible, compare it to a sample part and pattern that they can show you.

 

Good luck, BerTau

[Scott Bond]

Good Morning eveyone.

IMHO---All of what BerTau posted.

 

Bertau, Have fun, and Good luck in Chicago.The night life is almost the same as in L.A. ,but whach out for their Murder Mystery Train Ride thing.

 

[ 01-10-2003, 11:36 AM: Message edited by: Scott Bond ]

[BernieT]

Thanks Scott, it's getting closer!!! Brrrrrr!

 

Will be in Chicago all next week looking for house or apartment. Wife has small dog, wants washer/dryer in apartment, I want a garage and 2 bathrooms and no more than 10 miles to work. Wish me luck, I'm going to need it!!

 

Bernie

[dinoracer]

I used to make investment castings all of the time. IfI am correct we used 1.025 for the OD on brass and 1.028 on the ID's.

Sean

[Scott Bond]

Hey Surface

Did you ever get a result on this?

[Surface]

Scott,

I machined the model 7 percent larger and gave some of the parts to the foundry. They are going to make some sample castings for me and then I can measure the shrinkage.

I'm fortunate that the whole item is cosmetic and that as long as everything shrinks uniformly, everything will go together with the exeption of one part which must mate with a pre-manufactured part.

I'll let you know when I get the parts back

[Scott Bond]

Hi Surface

quote:

---

and that as long as everything shrinks uniformly

---

It will shrink similar to a rubber band.

[neurosis]

I guess that this is probably still relevant after 15  years?    

[Jayson Kramer]

Neurosis the 1.025 was more of standard to say Alum wax shrink. it really is not the same across the board for all metals.

I should stated that when I first answered this almost 15 years ago.. Are you doing a mold. I think my Brother inlaw Scott bond still knows most of the shrinkage's for a lot of them . I could ask.