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GUIDELINE TOLERANCES FOR HOT UPSET FORGINGS INTRODUCTION Fundamentally, impression die forgings produced on Horizontal Forging Machines (Upsetters) are similar to those produced by Hammers or Presses. Each is the result of forcing metal into cavities in dies which separate at parting lines. The impression in the ram-operated "Heading Tool" is the equivalent of a Hammer or Press top die. The "grip dies" contain the impressions corresponding to the Hammer or Press bottom die. Grip dies consist of a stationary die and a moving die which, when closed, act to grip the stock and hold it in position for forging. After each workstroke of the machine, these dies open to permit the transfer of stock from one cavity to another in the multiple-impression dies. After an operation establishes a final contour on a specific portion of an upset forging, subsequent operations may have some effect on that portion. Thus the number and sequence of steps used in shaping the forging must be planned in advance in order that overall tolerance may be anticipated. Most upset forgings begin with and retain some portion of a hot rolled bar. Permissible mill variations thus have an effect on upset forging tolerances. As a result of this and other technical considerations, tolerances applying to forgings produced on Forging Machines differ somewhat from those of Hammer and Press forgings. TOLERANCES 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 practicable 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 allowances 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. TOLERANCE ACCUMULATION Where applicable the enclosed tolerances are accumulative. (Example: overall length tolerance = flange thickness tolerance + stem length tolerance.) 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 IN THIS BOOKLET 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.
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