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### Circular Forgings Tight Tolerance Calculator per. EN-10243-1

Circular Forgings Tight Tolerance and Dimensions Calculator

Drop and vertical press forgings per. EN-10243-1 Forging grade E Tolerances for length, and diameter. Forging grade E providing closer tolerances to assist in accommodating those instances in which the normal manufacturing standards are inadequate. While grade E (close) tolerances may be applied to all dimensions on one forging, it is more economical to apply them only to those specific dimensions on which closer tolerances are essential. This grade should not be specified unless the additional forging cost entailed can be justified by a consequent saving in overall cost.

Information required in determining forging tolerances

To determine the tolerances applicable to a given forging the following information is required in addition to the dimensions of the forging:

• mass of forging;
• shape of die line;
• category of steel used;
• shape complexity factor;
• type of dimension.

Note: Tolerances are 2/3 and 1/3 (rounded values). Minus and plus signs, given in the table above, are applicable to external dimensions. For internal dimensions reverse the values.

The shape complexity factor takes account of the fact that in forging thin sections and branched components, as compared to components having simple compact shapes, larger dimensional variations occur which are attributable to different rates of shrinkage, higher shaping forces and higher rates of die wear.

Eq. 1
Shape complexity factor

S = mf / mes

Eq. 2

Volume of enveloping shape

v = l · b · h

Eq. 3
Non-Circular forging enveloping shape

mes = l · b · h · p

where

mf = mass forging
mes = Mass enveloping shape See figures 1 and 2
ρ = density (steel ~ 0.00785 g/mm3);
h = enveloping length;
l = enveloping length dimension;
b = enveloping width dimension;
h = enveloping height dimension
v = volume of enveloping shape

Enveloping shapes of non-circular forgings

Figure 1

Figure 2

The resulting shape complexity factor is determined as falling within one of the following categories:

S4: Up to and including 0,16;
S3: Above 0,16 up to and including 0,32;
S2: Above 0,32 up to and including 0,63;
S1: Above 0,63 up to and including 1.

Category of steel used

The type of steel symbol used takes account of the fact that steels of high carbon and high alloy content are more difficult to deform and cause higher die wear than do steels with lower carbon content and lower alloying elements.

The category of steel used is determined as being within one of the following:

• Group M1: Steel with carbon content not more than 0,65 % and total of specified alloying elements (Mn, Ni, Cr, Mo, V, W) not more than 5 % by mass;
• Group M2: Steel with carbon content above 0,65 % or total of specified alloying elements (Mn, Ni, Cr, Mo, V, W) above 5 % by mass.

To determine the category in which a steel belongs, the maximum permitted content of the elements in the steel specification shall be the values used.

Shape of die line

Figure 3 Shape of Die

Reference:

EN 10243-1 Steel die forgings Tolerances on dimensions, Part 1: Drop and vertical press forgings

Alternatively: BS EN 10243-1, Steel die forgings Tolerances on dimensions, Part 1: Drop and vertical press forgings

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