F. H. Meeder Sales Manager


P. F. Foley President


HARCAST COMPANY, INC.


If your design people specify a part to be "steel"; why not consider investment casting the part in one of the higher strength non-ferrous alloys- alumi- num, silicon bronze or beryllium copper. The end result will be a satisfactory part at a lower price, since non -ferrous alloys generally can be cast at a lower cost.


Walter A. Dubovick President


ENGINEERED PRECISION CASTING CO.


Machining operations can often be simplified by designing locating pads or tabs for holding castings in position for machining. For ex- ample, the three tabs in the design of this connecting rod support it in a true horizontal plane. Holes can easily be bored parallel to each other and the top surfaces ground par- allel to the three tabs. By using the tabs to keep the part level, the axis of each hole can be kept exactly perpendicular with the top surfaces.


CASTING ENGINEERS


The general tolerance rule of thumb, "plus or minus .005 inch per inch", is probably the most misunderstood con- cept among investment casting users.


Keep in mind that this "guideline" can vary up or down, depend- ing upon shape of part, alloy, quantity, and type of tooling. It is also based upon what can be reasonably done without selective inspection or extensive adjustment of tooling, either of which usually involves extra cost. It is also much easier to hold this range, or in some cases closer, if only the critical dimensions are restricted .


Also, this rule of thumb applies to absolute dimensions. It is not uncommon to have a run of castings fall within closer limits, but the range may not necessarily be equally spaced around the mean.


On smaller parts, (less than l" cubed) tolerance of plus or minus .003, and in special cases as low as plus or minus .001" are possible by secondary sizing - usually at extra cost. The quantity however must be sufficient to justify the additional or improved tooling required.


Leo E. Carr


Manager, Special Projects PRECISION


METALSMITHS, INC.


Frank Gobel Sales Manager


ELECTRONICAST INC.


In designing for investment castings, visualizing the part from the standpoint of good casting de- sign wil I save money. Take advantage of the design tips in the ICl's "How to Design and Buy Investment Castings" manual or from the Engi- neering Department of your casting supplier. Take advantage of the wide selection of metals that can be investment cast. Consider if the next operation can be reduced or eliminated by being incorporated as part of the casting. Conversely can part of the casting be more economically fabricated and added later? When designing a casting that will require secondary operations make special note of the first operation since aids to fixturing or driving can be cast in place.


This artificial mitral valve for the human heart was created by use of a Prototype Service. Its design concept, function, performance, and cost were established without tooling charges. Application of available foundry know- how permitted the designer to refine his original design concept to match service requirements of the valve with needs of the beating heart. Prior to human use, the valves were subjected to accelerated testing equivalent to 45 years actual service in the heart. The parts showed no appreciable wear or corrosion-investment castings are reliable.


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