Machining allowance: during the die forging process, the shape size of the forging are changed due to the wear of the forging die, the dislocation of the upper lower dies, the change of the slope of the die the volume of the blank, oxidation, decarburization the fluctuation of the final forging temperature during the heating process. The shape size of the forging fluctuate in a certain range. After die forging, all part of the surface of the forging still needs to be machined, so these surfaces have a metal layer for machining in the design, which is called machining allowance. The purpose of machining allowance design is to improve the surface quality ensure the dimension. The surface that needs machining on the forging drawing. There's a margin. The size of machining allowance is related to the shape complexity, dimensional accuracy, surface finish, forging material die forging equipment.

Forging tolerance: in the process of die forging, due to under pressure, metal filling the groove, die wear deformation, inaccurate selection of forging shrinkage rate during die design, manufacturing tolerance of final forging groove, accuracy change of forging equipment, die dislocation, manual operation error other reasons, the actual size of forging can accurately reach the nominal size of forging, there should be a certain size error Difference is called forging tolerance. The tolerance of forgings shall be designed indicated no matter whether they are machined . The tolerance of forgings mainly includes the tolerance of length, height width direction, thickness tolerance, straightness flatness tolerance, center distance dimension tolerance, coaxiality tolerance, residual lateral burr tolerance, penetration depth tolerance, longitudinal burr tolerance punching deformation tolerance.

Forging surplus block: in the process of die forging process design, for the parts which are difficult to forge such as small holes, narrow grooves, steps with small diameter difference, etc., can be designed. The design of surplus forging block can simplify the shape of forging reduce the difficulty of die forging, but it will increase the cost of machining metal consumption. The design of the remaining block should be considered according to the shape of the parts, the level of die forging the degree of machining difficulty. For some forgings that require microstructure mechanical properties testing, it is necessary to design the residual pieces of the sample for testing the microstructure mechanical properties of the forgings. For the forgings with special requirements in heat treatment machining, it is necessary to design the rest of the collet.

Determination method influencing factors of forging machining allowance: there are mainly two methods to determine machining allowance tolerance: one is determined according to the shape size of forgings, the other is determined according to the tonnage of die forging hammer.

The tolerance of forgings can be divided into dimensional tolerance, shape position tolerance surface technical requirement tolerance. Dimensional tolerance mainly includes length, thickness, width, center distance, angle, forging die slope, fillet radius arc radius. Shape position tolerance includes straightness, flatness, coaxiality, displacement, shear end deformation rod deformation. The surface technical tolerance includes the size of the shearing burr, the depth of the indentation of the ejector pin the surface roughness.