GB/T 12362-2016 in English

《GB/T 12362-2016钢质模锻件 公差及机械加工余量》由TC74（全国锻压标准化技术委员会）归口，主管部门为国家标准化管理委员会。

ChinaStandards.net is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.

This standard was drafted in accordance with the rules given in GB/T 1.1-2009.

This standard replaces GB/T 12362-2003 “Steel Die Forgings-Tolerance and machining allowances”. Compared with GB/T 12362-2003, except for editorial changes, the main changes are as follows:

- Replace the “Machine Machining Margin and Its Usage Principle” in the scope with “Machine Machining Remaining Level and Technical Content”, and change the “Structured Steel Forgings” to “Structural Steel Die Forgings” and replace “250kg” with “500kg”. (See Chapter 1, Chapter 1 of the 2003 Edition.)

- Remove "forgings that required additional manufacturing processes to be achieved" and "flat forged parts used only at ordinary level" (see 2.1 in 2003)

In the special case a) of 3.1.2, “In selecting tolerances, the mass of the forging is considered only the mass of the cylindrical part of diameter d and thickness t; if this special rule selects a tolerance less than that of 3.1.2 Tolerances selected by the rules are selected according to the general rules of 3.1.2” is added (see 3.1.2).

In the special case b) of 3.1.2, the “Where selecting the dimensional tolerances of the relevant features, the quality of the forgings only considers the mass of the cylinder with a diameter of d1 and a thickness of t1; if the tolerances chosen for this special rule are less than .2 Tolerances for general rules are based on the tolerances selected in 3.1.2 General rules (see 3.1.2) is added;

Remove “Where using coal-fired or secondary-fired heating, consider increasing the tolerance or margin appropriately, the value of which shall be determined through negotiation between the supply and demand sides” (see 3.1.6 of the 2003 edition).

Change "error tolerance" to "error" (see 3.2.4, 2003 version 3.2.4)

Change "deep tolerance" to "depth" (see 3.2.14, 2003 version 3.2.14)

The quality ranges in Table 1, Table 2, Table 3, Table 4, and Table 16 are revised and the query lines are added (see Table 1, Table 2, Table 3, Table 4, Table 16, Table 1, Table 2 of 2003 Edition), Table 3, Table 4, Table 16)

The aperture range in Table 15 is modified and the query line was added (see Table 15, Table 15 of the 2003 Edition).

This standard was proposed and is under the jurisdiction of the National Forging Standardization Technical Committee (SAC/TC74).

The previous versions of the standards replaced by this standard are:
- GB/T 12362-1990, GB/T 12362-2003.



Steel Die Forgings-Tolerance and Machining Allowance
1 Scope
This standard specifies the steel die forgings (hereinafter referred to as "forgings") tolerances and machining allowance levels and technical content.

This standard applies to die forging hammers, hot die forging presses, screw presses, flat forging machines and other forging equipment production of structural steel die forgings.

Other steel forgings can also be used as reference. This standard applies to forgings with a mass less than or equal to 500kg and a length (maximum size) less than or equal to 2500mm.
2 Level of Tolerances and Machining Allowances

2.1 The tolerance is divided into two levels: ordinary level and precision level.
Ordinary tolerances apply to forgings that meet the technical requirements of general die forging processes.

Precision tolerances apply to forgings with higher technical requirements and can be used for the full size of a forging and for local dimensions.

2.2 The Machining Allowance is Only One Level.

3 Technical Content

3.1 The main factors to determine forging tolerance and machining allowance

3.1.1 Forging Mass mf
Forging quality are estimated according to the following procedure:
The basic dimensions of the part drawing → Estimate the machining allowance → Draw the forging drawing → Estimate the forging quality, and determine the tolerance and machining allowance according to this quality check table.

3.1.2 Forging Shape Complex Factor S
The forging complex shape factor is the ratio of the forging mass mf to the corresponding forging external shell mass mN, see Equation (1):
S=mf/mN (1)

The forging profile containment mass mN is the calculated mass of the cylinder or cuboid containing the largest profile of the forging as the entity, and is calculated according to formula (2) or formula (3):

a) Round forgings (Figure 1)
mN=1/4·π·d2·h·ρ (2)

Where:
ρ——Steel density(7.85g/cm3)




Figure 1 Round Forgings 

b) Non-circular forgings (Figure 2)
mN=l·b·h·ρ (3)



Figure 2 Non-circular Forgings

According to the size of S value, forging complex shape factor is divided into 4 levels:
S1 level (simple): 0.63 S2 level (general): 0.32 S3 level (complex): 0.16 S4 level (complex): 0
Special case:
a) Where the forging is in the form of a thin disk or flange (Fig. 3), and the thickness and diameter ratio of the disk is t/d ≤ 0.2, the S4 class is used; where selecting tolerances, the mass of the forging only considers the mass of a cylindrical part with the diameter d and a thickness of t; if the tolerances chosen for this particular rule are less than the tolerances selected according to the general rules of 3.1.2, the tolerances shall be chosen according to 3.1.2 General Rules.




Figure 3 Flange Pieces
b) Where the flat forgings t1 / d1 ≤ 0.2 or t2 / d2 ≥ 4, the use of S4 level (Figure 4); Where selecting the dimensional tolerance of the relevant features, the forging mass only considers the mass of the cylindrical part with the diameter of d1 and thickness t1; if the tolerance selected for this particular rule is less than the tolerance selected in accordance with 3.1.2 General Rules, then the tolerance selected in 3.1.2 General Rules shall prevail.


Figure 4 Flat Forgings

c) Where the punching depth of the flat forging is greater than 1.5 times the diameter, the complex shape factor is increased by one step.

3.1.3 Forging Quality Coefficient M
Forging material coefficient is divided into two levels: M1 and M2.

M1 level: Alloy steel with a total carbon content of less than 0.65% and a total content of carbon steel or alloy elements of less than 3%.

M2 level: Alloy steel with a maximum carbon content of 0.65% or more and a total content of carbon steel or alloy elements greater than or equal to 3%.

3.1.4 Forging Parting Line Shape

Forging split line shapes are divided into two categories:

b) Asymmetrically curved parting line [Figure 5c)].



Figure 5 Forging Parting Line Shape
3.1.5 Part Surface Roughness
The surface roughness of parts is an important parameter for determining the allowance of forgings. This standard is divided into two categories according to the size of the arithmetic mean deviation of the Ra:

a) Ra≥1.6μm;
b) Ra<1.6μm

3.1.6 Forging Heating Conditions
The heating conditions for forgings referred to in this standard are electricity, oil or gas (natural gas).

3.2 Tolerance

3.2.1 Length, Width and Height Dimension Tolerances

3.2.1.1 Length, width, and height dimension tolerances are dimensional tolerances along the length, width, and height of the same mold on the parting line side (Figure 6). Such tolerances are determined by look-up tables based on the basic dimensions, mass, shape complexities, and material coefficients of the forgings. Table 1 is an ordinary grade, and Table 2 is a precision grade.


Keys:
l1, l2 - length dimension;
b1, b2, b3, b4 - width dimension;
h1, h2 - height dimension;
f - drop size;
t1, t2 - thickness dimension across the parting line
Figure 6 Forging Size Representation

3.2.1.2 Drop (f in Figure 6) dimension tolerance is a form of height dimension tolerance. The value is wider than the corresponding height dimension tolerance by one block, and the upper and lower deviation values are distributed by ±1/2.

3.2.1.3 Aperture size tolerance
Tolerance values are determined from Table 1 or Table 2 according to the aperture size. The upper and lower deviations are assigned in +1/4 and -3/4 ratios.

3.2.2 Thickness Tolerance

The thickness dimension tolerance refers to the tolerance of the thickness dimension across the parting line (t1, t2 in FIG. 6).

All thickness dimensions of the forgings are taken to the same tolerance, and the values are determined by Table 3 or Table 4 according to the maximum thickness dimension of the forgings.

3.2.3 Top bar indentation tolerance

The indentation tolerance of the ejector rod is determined by Table 3 or Table 4. The protrusion is positive and the recess depth must not exceed the depth tolerance of the surface defect.

3.2.4 Mismatch
The mismatch is the distance that the forging offsets on the parting line and the corresponding points of the next two parts (Figure 7). The value is calculated according to Formula (4):
Mismatch= or (4)
Where:
L1, b1 - the maximum projection length and width parallel to the parting line;
L2, b2 - the minimum projection length and width parallel to the parting line.
The mismatch is determined by Table 1 or Table 2, and its application is independent of other tolerances.


Figure 7 Mismatch

3.2.5 Horizontal residual flash and cut-in depth tolerances
After the forging is trimmed, the tolerance of its horizontal residual flash is determined by Table 1 or Table 2, and the depth tolerance of the forging is equal to the tolerance of the horizontal residual flash. Both have nothing to do with other tolerances (Figure 8).




a) Residual flash b) Cut-in depth
Figure 8 Residual Flash and Cut-in Depth

3.2.6 Method of Using Tolerance Table
Where determining the forging length, width or height dimension tolerances from Table 1 or Table 2, the appropriate range should be selected based on the forging mass and then moved to the right along the horizontal line. If the material coefficient is M1, it will continue to move to the right along the same horizontal line; if the material coefficient is M2, it will move down the slope line to the intersection with the vertical line of M2. For the complex shape factor S, in the same way, move horizontally or diagonally to the position of S1 or S2, S3, and S4, and continue moving to the right until the vertical column of the required size, you can find the desired tolerance value.

Where determining the misalignment and lateral residual flash tolerances, the same range is selected in the forging mass field and then moved to the left to determine the misalignment and residual flash edge tolerance values based on the parting line shape.

Example: a forging 6kg, length dimension 160mm, material coefficient M1, shape complex factor S2, straight parting line, using ordinary level tolerances, limit deviation found in Table 1, lateral residual flash edge tolerance 1.2, difference For 1.2, the table lookup order is shown by the arrow in Table 1.
The remaining tolerances use method of analogy.

Foreword i
1 Scope
2 Level of Tolerances and Machining Allowances
3 Technical Content
Annex A (Informative) Forging Tolerance Application Example