Reprinted from


Meta Mo IL


Pre FEBRUARY 1965 Use investment tastings for . . .


PARTS THAT MUST NOT FAIL


By W. A. KELLER, purchasing agent Accessories Div., Parker-Hannifin Co.


The requirement for uniform properties, complex shapes, and hard-to-machine alloys called for castings. The dimensional accuracy, good as-cast surfaces, and structural integrity dictated investment castings.


B ECAUSE FAILURE of a component can mean loss of life as well as the loss of a multi-million dollar aircraft, Parker-Hannifin uses in- vestment castings in jet engine components. Why castings at all? Because many of the alloys we use are either unmachinable or exh·emely expensive to machine except by grinding; many operate at high temperatures. Through experience, we have learned that the investment casting process will give us high iilltegrity castings time after time. The process will ho,ld the dimensional toler- ances we require, will meet any X-ray requirements for soundness, and can form inrtricately cored passages when they are required. There is little danger of core shift; sand inclusions are not a trouble nor are burrs and voids. Yet all of these troubles are more or less common with other casting methods; even the Shaw process has not been too successful on the type of castings we require. Futher, due credit must be given the men who have built up the investment casting industry. Only a few years ago it was impossible to accept their claims for what they could do. Today they have become highly realistic. They know the limitations of the process and the limitations of their own foundries. They recognized the need for good metallurgical skill and knowledge and wenrt: out and got it. It has been our experience that each foundry has specialized to some exteillt. Within its field of specialization each foundry can do, and generally does do, fine work. For example, we have found that the companies which spe~ cialize in blade and vane castings will, generally, do best on very high integrity castings with tight, difficu1t control. Other foundries do ex- cellent wmk if coring is simple, but are not able to compete when complex coring problems ar involved. Still other companies are special- cialists in using soluble cores and preformed cores. It's because of this wide divergence in ability and specialization that


we have frequent clinics for our design engineering groups. We fre- quently will ask an investment casting foundry to come in and put on a clinic so that our engineers can learn the capabilities of the process and the individual foundry. During design we often ask knowledgeable investment casters for ad-


vice and help. The only limit we put on modification of a design to improve castability is function. Just as long as a part will do its job, not weigh too much, and of course, not cost too much we will modify it to improve castability. (continued)


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