Tolerance Calculator Grade E Wall Thickness and Ejector Marks

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Tolerance Calculator Grade E Wall Thickness and Ejector Marks

Tolerances, Engineering Design & Limits & Fits
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Wall Thickness and Ejector Marks Tolerance Calculator Grade E per. EN-10243-1 for Circular Forgings

Grade E per. EN-10243-1 is for 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. This Standard does not include ranges of special tolerances closer than grade E. Such requirements usually necessitate supplementary operations, e.g. hot or cold coining or special processes such as warm or cold forging.

Information required in determining forging tolerances

Tolerances for thickness, based on the greatest dimension of thickness, are obtained from the appropriate table for the grade required by the same method as that described above for length, width and height 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 = m_f / m_es

Eq. 2
Circular mass enveloping shape

m_es = π · ( d² / 4 ) · h · ρ

where

m_f = mass forging
m_es = Mass enveloping shape See figures 1 and 2
d = diameter;
ρ = density (~0.00785 g/mm³);
l = length dimension;
h = diameter dimension

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.

Enveloping shapes of circular forgings

Enveloping shapes of circular forgings
Figure 1

Enveloping shapes of circular forgings
Figure 2

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