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9. APPENDICES GUIDELINE TOLERANCES FOR CUSTOM FORGINGS The purpose of this information is to make available to purchasers, producers, consumers and all other interested persons,
information concerning the manufacture of forged parts or products on the basic types of mass production forging equipment.
The information contained herein regarding tolerances, inspection and measurement procedures and related subjects substantially
represents the manufacturing standards and practices of the many producers of forged parts or products as reported to the Association or as obtained
from other scientific and technical sources. This Appendix contains modified versions of the previously published tolerance guidelines offered by the Forging Industry Association.
This section is divided into four subsections of guideline tolerances as follows: A _ TOLERANCES FOR IMPRESSION DIE FORGINGS TOLERANCES for impression die forgings There are practical limitations in dimensions and other
characteristics of forged parts or products which vary according to the part or product and the producer's equipment. The degree of precision
attainable in the manufacture of forged parts or products is dictated by the essential character of forging equipment and unavoidable contingencies
in forging operations. Theoretical exactness is seldom attained, and it is therefore
necessary to make allowance for deviations. The tolerances set forth herein represent what the Forging Industry Association believes to be typical
within the industry, as determined by actual measurements of forgings produced under normal operating conditions on standard forging equipment. Experience within the industry shows that dimensional
variations in forging are commonly functions of the dimensions involved, and the tolerances herein are based upon this observed fact. The experience of producers and purchasers of forged
parts and products indicates that the tolerances set forth herein will provide adequate dimensional accuracy for most applications. THE TOLERANCES OUTLINED HEREIN ARE GUIDELINES BASED ON
HISTORICAL, AVERAGED DATA. THE TERMS OF EACH TRANSACTION BETWEEN A FORGING PRODUCER AND A PURCHASER, INCLUDING TOLERANCES APPLICABLE TO THAT TRANSACTION,
MUST BE NEGOTIATED AND CONFIRMED IN ADVANCE OF PRODUCTION. There are several special ways of providing closer tolerances
on selected dimensions on forgings with added operations. These include, cold and warm coining to achieve closer thickness tolerances, using special
pressure padded trimmers for improving straightness, cold sizing of holes for improved tolerances on hot pierced holes, and warm forging as a manufacturing
process. Be sure to contact technical personnel at your forging source for help in determining such special capabilities. |