Investment Casting

[ronaldlee]

Can anyone explain what Investment Casting is? How does it differ from other forms of casting and which manufactuers use this process , besides Ruger ? Thanks for any information or opinions on this process--------------Ron

[Val]

Very briefly and simplified, an investment casting is one in which a mold is made for each individual part as opposed to other casting processes where multi parts are made from a mold. The result is a very consistent very dimensionally accurate casting. Investment castings are used a lot in the Aerospace Industry where accurate cast machined parts are required. It is a more expensive casting process than many of the others.

[Keith L]

Investment casting is also known as lost (some other material such as foam or wax) casting.  A mold is made then filled with wax, foam. salt or some other medium to make an exact copy of the part to be made.  This is then covered with a slurry.  When the coating is dry the positive model is placed into a box and foundry sand is packed around it.  Normally the positive model has "runners" attached to it, passages for molten metal to flow into the sand filled box.  When the molten metal is poured into the runners the wax or other material burns out and the metal flows into the negative mold created in the sand.  The metal is allowed to harden, then the rough cast part is removed.  Carefully made original models for the wax (or other material) allow castings to be close to the proper size that require less machining than some other casting methods.

Another form of casting is die-casting, commonly done when casting aluminum or zinc.  Molten metal is forced under pressure into a mold made of steel.  Many alloy framed pistols have die cast frames.

All types of casting have to be done carefully, with a method for getting the molten metal into the form at the proper speed and temprature to take the form of the mold and not to be filled with air bubbles.  Air can cause weakness and small holes in the final part.

I can't help you with all the gun parts that are cast.  I know that many parts in TC guns are made in their casting operation.  I expect it is investment casting.  Other cast items are the engine blocks in cars, boats, and anything else with an engine. Transmission cases, differential housings, many machine parts, etc.  Lots of things are cast.  It is far less time consuming than making parts like this from solid hunks of metal and removing lots of it to get the final form.  Well done castings are strong and will last a long time.

I hope this helps a little.  I did lots of consulting over the past ten years in foundries, including one that made many gun parts.

[ronaldlee]

Thanks for the replies. I have been a little shy of anything made of cast anything. I'm sure there have been many improvments in the process since the late 50's [I think] when I dropped an old High Standard 22 /9 shooter on a concrete floor and it broke in half.-----------Ron

[quickdtoo]

Here's a good read on investment casting as it applies to the firearms industry.

Tim

http://www.castsolutions.com/archive/08_feature_article.html

[Keith L]

Cast zinc used to be called pot metal and was not particularly sturdy.  It was easy to cast however, and many things were made of zinc giving cast metal a bad name.  Castings also have to be properly made of the right metal chemistry to be sturdy.  When done well they are great.  Done wrong they are junk, like many other things.  Right now there are some real revolutionary things happening in casting, with one of the most advanced aluminum foundry in the world making castings for the boat motor industry, and it is happening here in America.