1 End use required a casting in a non-machinable alloy (N-155). Invest- ment casting is the only method of production that can insure dimensions, surface, and reliability.


3 Here the foundry broke a .... complex shape into relatively , simple investment castings (below), simplified machining, and improved operation.


2 Burrs or flash that might break loose could damage, even ruin a jet engine. The Stellite 6 investment casting above avoided this.


The clinics and the consultation have another most desirable result. When a part is put out for bids there is seldom a wide spread in unit costs. Where we find the greatest spread is in tooling costs. Some companies try to cut tooling costs and end up with poor quality tools that go off tolerance after short use. Frankly we are suspicious of any bid where the tooling charges are materially lower at one foundry than at others which bid on the same job - we expect trouble due to cheap tooling. Now let's look at just a few castings in current use.


The first one, figure 1, is an aircraft part cast in Haynes alloy N-155. This alloy is practically impossible to ma- chine and yet the part configuration requires quite in- tricately cored passages. The cored holes must have smooth inside surfaces and be free of any obstructions. Grinding is the only second operation that can be done. The part is used pretty much as-cast. The next part, figure 2, is a fuel injection nozzle for


the J-79 jet engine. It's cast in Stellite 6. Again this is a part that is unmachinable and with tiny cored holes which must be accurately placed, smooth and free of burrs and obsb·uctions and the casting must be sound. Any flow impediment can cause flame-out of the en- gine with loss of lives and the aircraft. This part is so critical that it is 100% inspected at a magnification of lOX to insure against flash and loose metal.


The castings shown in figure 3 are in l 7-4PH, a very machinable alloy. Shape is the determing factor here. While some of the parts could, of course, be machined from bar stock the cost would be too high. Other parts of this assembly could not be machined; in fact the most complex shapes are not shown in the illustration. This particular part was originally designed as a


single casting to be made in either sand or Shaw molds. The results were not good. Misruns, incomplete fill, inclusions, core shift, porosity, and many other faults were common. Even usable castings were so rough that the cost of machining was excessive. Now as originally designed there were innumerable


cored arms sticking out of the main casting. The part was conceived as a single casting. When we called in an investment casting engineer ·the first suggestion he made was to break the single complex part down into a number of smaller, simpler parts. This is di- rectly opposite to the usual recommendations for a cast part. As a result of the recommendations the various parts


are now easily cast and meet all of our specifications. Machining is simple and inexpensive and we seldom have to reject a part because of foundry failure. As a result of favorable experience with the parts illustrated and with many others we confidenrtly de- sign for investment casting whenever possible. PMM


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