Standard Tolerances for Drop Forgings

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Standard Tolerances for Drop Forgings

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Tolerances adopted by the Drop Forging Association in 1937 apply to forgings under 100 pounds each. Forging tolerances may either be “special” or “regular.” Special tolerances are those which are particularly noted in the specifications and may state any or all tolerances in any way as required. Special tolerances apply only to the particular dimensions noted. In all cases where special tolerances are not specified, regular tolerances apply.

Table 1a. Standard Tolerances for Forgings Adopted, 1937, by Drop Forging Association for Forgings under 100 Pounds Each

Thickness tolerances apply to the over-all thickness. For drop-hammer forgings, they apply to the thickness in a direction perpendicular to the main or fundamental parting plane of the die. For upset forgings, they apply to the thickness in the direction parallel to the travel of the ram, but only to such dimensions as are enclosed by the actually formed by the die.

Table 1b. Standard Tolerances for Forgings Adopted, 1937, by Drop Forging Association for Forgings under 100 Pounds Each

For each additional inch under shrinkage, add 0.003 to the commercial tolerance and 0.0015 to the close tolerance. For example, if length or width is 12 inches, the commercial tolerance is plus or
minus 0.036 and the close tolerance plus or minus 0.018.
For each additional 2 pounds under die wear, add 0.003 to the commercial tolerance and 0.0015 to the close tolerance. Thus, if the net weight is 21 pounds, the die wear commercial tolerance is 0.062
plus or minus, and the close tolerance 0.031 plus or minus.
For each additional 6 pounds under mismatching, add 0.003 to the commercial tolerance and 0.002 to the close tolerance. Thus, if the net weight is 37 pounds, the mismatching commercial tolerance is
0.033 and the close tolerance 0.022.

Table 1c. Standard Tolerances for Forgings Adopted, 1937, by Drop Forging Association for Forgings under 100 Pounds Each

Table 1d. Standard Tolerances for Forgings Adopted, 1937, by Drop Forging Association for Forgings under 100 Pounds Each

These quantity tolerances represent the permissible over-run or under-run allowed for each release or part shipment of an order. Any shipping quantity within the limits of over-run or under-run shall be considered as completing the order.

Table 1e. Standard Tolerances for Forgings Adopted, 1937, by Drop Forging Association for Forgings under 100 Pounds Each

Regular tolerances: are divided into two divisions — “Commercial Standard” and “Close Standard.” “Commercial Standard” tolerances are for general forging practice, but when extra close work is desired involving additional expense and care in the production of forgings, “Close Standard” may be specified. When no standard is specified, “Commercial Standard” shall apply.

Regular tolerances are applicable to 1) thickness; 2) width, including shrinkage and die wear, mismatching, and trimmed size; 3) draft angle; 4) quantity in shipment; and 5) fillets and corners.

Thickness Tolerances: Thickness tolerances shall apply to the overall thickness of a forging.

Width and Length Tolerances: Width and length tolerances shall be alike and shall apply to the width or length of a forging. When applied to drop hammer forgings, they shall apply to the width or length in a direction parallel to the main or fundamental parting plane of the die, but only to such dimensions as are enclosed by and actually formed by the die. When applied to upset forgings, they shall apply to the width or length in a direction perpendicular to the direction of travel of the ramp.

Width and length tolerances consist of the three subdivisions following: a) Shrinkage and die wear tolerance; b) mismatching tolerance; and c) trimmed size tolerance.

Reference:
Drop Forging Association