The greater the strength (or hardness) of the material, the greater the fine punching force, the easy deformation of the die, the easy breakage of the weak punching element, and the easy chipping of the cutting edge. Therefore, the greater the strength of the material, the greater the difficulty of fine blanking; the greater the elongation of the material, the less likely it is to tear and peel off the punched surface, and it is easy to obtain a smooth punched surface, and the difficulty of fine blanking is small; the smaller the particles of carbide structure ( It is best to be fine-blanked), the easier it is to fine-blank, mainly to obtain a smooth and clean punched surface; the greater the anisotropy of the material, the more difficult it is to ensure the dimensional accuracy of fine-blanking parts, especially for large-scale fine-blanking parts.
In general, low carbon steel and low carbon alloy steel are less difficult to fine blanking; medium carbon steel and medium carbon alloy steel are moderately difficult to fine blanking; while high carbon steel and high carbon alloy steel are more difficult to fine blanking.
In the fine blanking of medium and high carbon steel, in most cases, the material needs to be spheroidized, and in order to control the thickness tolerance, it is necessary to select the material in the cold-rolled state, so the "cold-rolled spheroidized state" is used for fine blanking. normality of material.
The dimensional accuracy (including shape and position accuracy) of fine blanking parts is higher than that of ordinary blanking parts, which is also the advantage of the fine blanking process. However, fine blanking also has its limitations. During the fine blanking process, the material around the blanking surface will be deformed by tension or compression, forming a certain internal stress. After demolding, the internal stress is released, resulting in inconsistent parts size and mold size.
The size of this dimensional change is related to many factors, such as the strength of the material, the stiffness of the mold, the size of the mold edge fillet, the size of the blanking gap, the blank holder force and the back pressure, and the roughness of the mold cavity. And the type of lubricating oil, the structure and shape of parts, etc.
It is precisely because of the influence of so many factors that if the dimensional accuracy of fine blanking parts is too high, the process capacity will be very low, and the difficulty of fine blanking will naturally increase.
Of course, the effect of each of the above factors on the dimensional accuracy is very small and limited to the microscopic range, which is also the reason for the high precision of fine blanking parts.
Generally speaking, if the accuracy level is greater than IT12, it is easy; between IT8 and IT12, it is medium, and if it is less than IT8, it is difficult.
The measures to improve the precision of fine blanking parts are nothing more than considering its main influencing factors. Usually the rigidity of the die, blanking gap and edge fillet are the keys. Sufficient die rigidity, reasonable blanking gap and edge fillet that does not produce shearing surface tearing are the keys to punching high-precision parts. important premise.