investment cast 4130?

[X2cnc]

I need to make some small parts from steel such as 4130. They're about the size of one of a pair of standard dice, maybe 1/2" in the longest dimension, of very complex shape. It would take several setups and some special fixturing to make them, but only two of the dimensions are critical.

I have a book called "Lost Wax or Investment Casting" by James E. Sopcak. It was printed in 1986 from article apparently written in the 1950s or 1960s. He describes a homebuilt setup for making small investment castings in gold, silver, or bronze. His method (which may be quite common, for all I know...) is to cast the investment, burn out the wax pattern, and then put a piece of metal in a depression on the top of the investment, with a very small sprue. He heats the metal with an oxyacetylene torch, then uses a fixture with compressed air to force the molten metal into the mold. Surface tension keeps the metal from filling the investment until forced in by air.

There's no separate furnace, crucible, or handling of the molten metal; it's all done right on the mold.

This is all described in basic DIY fashion, and I'm particularly interested because I have most of the materials to follow the book on hand. However, I'm curious if there might be a problem with trying to cast 4130 this way. It's a gas-weldable alloy, and Sopcak recommends a neutral flame.

All of the ferrous hobby-casting stuff I've found seems to be oriented toward iron, for ornamental use or engine castings...

Has anyone here cast steel this way? Is there a cheaper/better/simpler way?

[awerby]

The plaster/silica investment mixture used for casting silver, gold and other non-ferrous metals won't work for steel - the temperature is too hot, so the plaster would burn, causing a lot of gas to evolve in your casting. Actually, this would also be a problem even with non-ferrous metals, using the method you describe which attempts to short-cut the process by using the pour-cup as a crucible.

You'd either have to figure out something else to substitute for the gypsum plaster, or use the ceramic shell method, which is considerably different although it's still called lost wax investment casting.

Really, it's not worth setting up just for a few small parts. I'd say send them out to a foundry that specializes in investment casting of steel.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[miljnor]

I know I have gotten stainless cast in an investment casting before so that's poor advice.

It has been a long time but I believe you can cast anything with investment casting that you can with normal casting...just smaller run and more accuracy

[Geof]

Investment casting does not remove the need for intricate machining because you need to make the mold for casting the wax. If you are only make a few parts (<10) it is possible that machining them from scratch could be the best approach.

[X2cnc]

I think I can add a few heavy coats of paint to my sample part to compensate for shrinkage. As long as the relationship between two of the surfaces leaves enough metal to finish, the rest of the shape isn't all that critical.

[tony978]

If you get the right investment mix for your working temp and understand .
you need to burn out the wax and then pour into the mold when is hot with steel. Last but not least safety gear !!

good luck