During the production process of precision die forging, machining allowance shall be given to machined parts. For some important bearing parts, 100% sampling test or necessary process allowance is required for inspection and machining positioning. In the actual die forging production, due to the influence of various process factors, the actual size of the forging cannot be equal to the nominal size, and there will be deviations in both the height direction and the horizontal direction, so a certain deviation range is allowed for the forging. Forgings larger than the nominal size of forgings are positive tolerances, and forgings smaller than the nominal size of forgings are negative tolerances.
Tolerance classes for precision die forging
The tolerance of precision die forging is divided into two levels. General tolerance refers to the precision tolerance that can be achieved by general die forging methods; Precision tolerance, high dimensional accuracy, suitable for precision forgings. Forging quality: the forging quality shall be calculated according to the nominal size of the forging drawing, and the tolerance and allowance shall be determined according to this quality table.
Shape complexity coefficient of precision die forging: The shape complexity coefficient of forging S is the mass MC ratio of the forging quality M and the corresponding forging shape inclusion, that is, S=M forging/MC. Mold surface shape: mold surface shape is divided into two categories: one is straight mold surface and symmetrical bending mold surface, and the other is asymmetrical bending mold surface. Forging material coefficient: the forging material coefficient is divided into two levels: M1 and M2. M1 is a kind of carbon steel or alloy steel, with carbon content less than 0.65%, high carbon steel content and total content less than 3.0%. M2 is an alloy steel with carbon steel content greater than or equal to 0.65% or total alloy element content greater than or equal to 3.0%.
When precision die forging is used, if medium frequency induction heating or contact electric heating is used, the tolerance grade and allowance value shall be increased. When coal heating or two fire heating is adopted, the tolerance and allowance can be appropriately increased. The added value shall be determined through consultation between supply and demand.