This Instrument Mount . ..


is another instance where cooperation between the design engineer and the investment foundry resulted in a less costly yet functionally better casting than its fabricated predecessor. The original- design called for the part to be made by brazing together the machined flange and four bosses. In order to hold elliptical holes in the bosses within finished part tolerance, the bosses as well as the holes bored into the flange to accommodate them had to be held to very close tolerance; tolerances beyond the capability of casting. The buyer solved the problem by bringing the engineer and the investment foundry together. It was decided that since the bosses were to be cast in place, the necessity for close tolerances between the bosses and hole size was eliminated. Further review of the part's function enabled the design engineer to assign a total tolerance for location of the slotted holes acceptable to the casting producer. The casting, produced from 303 stainless, required finishing only at the flange I.D. plus grinding the bottom of the flange and top of the bosses.


CONCLUSION: The success of the parts we have described is


due to one common trait. Close cooperation between the designer, buyer and producer. These examples show that the designer or buyer


must know the part and its application thoroughly, otherwise, no agreement can be reached if design changes or compromise are necessary.


The buyer must be ready to spend enough money to guarantee results; no penny-pinching on production tools, checking fixtures, or supplementary equipment that may be required. The prospective producer must show competence on similar parts or at least on parts having some key features. If the producer can not demonstrate such competence, both parties should clearly set forth where responsibility starts and ends.


If the part doesn't work out with one producer, scrap the tools built and start over. The same tooling usually produces the same problems and the same failure.


Don't try to cast details which can be provided better by other means.


If two or more parts must be cast to fit without machining operations, be sure that one producer casts all parts. If they don't fit, there won't be any arguments over responsibility.


Above all, don't try to get more than one firm into the act through multiple bidding. It costs over a hundred dollars to send a competent engineer to help design a casting for you. If the job doesn't materialize, his firm will chalk it up to education. If it does, it's only fair to give his firm a chance to recover this cost.


Other significant case histories on how investment castings can save you money. > > > > > 9


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