The characteristics, mechanism, requirements and materials of the fine cutting die are preliminarily analyzed, especially the wear mechanism of the fine cutting die is carefully analyzed, and the protective measures to reduce die wear and ways to improve the Service life are presented from the aspects of wear shape and die clearance.
The proportion of thin blanks in industrial production is increasing, so the requirements for molds are increasingly greater.
How to extend mold life, reduce wear, reduce costs and increase economic benefits are the problems that most concern manufacturers.
There are many factors that affect the service life of the die, and wear is the most important factor that affects the service life of the die.
This post attempts to further analyze and discuss the die wear and protection mechanism.
1. Features of fine blanking technology
The fine suppression technology adopts micro gap, crown pressure plate and ejector plate on the female die to play the role of anti-female die, which can make the stamping parts achieve high dimensional accuracy and surface roughness.
In some developed industrial countries, the machining precision of the mold industry has reached the micron level, which can replace cutting under certain conditions.
Fine blanking technology has the following advantages.
1) The dimensional accuracy of fine cutting parts can reach IT7 ~ IT8, and the surface roughness of the shear section Ra is 2.4 ~ 0.4μm, with high perpendicularity and parallelism;
2) Compared with cutting, fine cutting technology can generally improve work efficiency by 10 times;
3) It can save a lot of electrical energy consumed by machine tool cutting and machining. The surface of the workpiece after fine cutting is hardened and the subsequent quenching process can be cancelled;
4) Composite fine stamping process can be used to simplify the forming process and combined with other forming processes such as bending, extrusion, stamping, etc.
The parts produced represent more than 20% of all fine-cut parts.
2. Fine suppression technology mechanism
The fine cutting process consists of adding rounded corners to the edge of the die and reducing the gap between the concave and convex dies.
In addition, the crown pressure plate and ejector are also added.
In order to restrict the tearing of materials before blanking and ensure the smooth progress of plastic deformation, metal materials need to be subjected to static pressure in the blanking deformation area, and the material is in the state of three-dimensional compressive stress (blanking force , blank holder force, back pressure), which is a necessary condition for fine blanking.
During fine cutting, the workpiece holder presses the material to prevent material outside the shear deformation zone from flowing with the punch during the shearing process.
The supporting effect of the blank holder and reverse pressing plate, together with the small gap between the convex and concave dies (generally 0.5% of the material thickness and 1/10 of the common blanking), makes the workpiece firmly pressed to avoid tensile stress caused by warping of the part, resulting in brittle fracture, thus forming a shear strip of plastic material.
If necessary, the three-dimensional compressive stress tensor in the deformation area can be increased to improve the plasticity of the material.
The punch press and cutting die tip can be rounded to reduce the stress concentration at the tip, avoid the generation of cracks, improve the stress state in the deformation area, and obtain bright cutting vertical surface section and cutting parts with small slope, flat surface and high dimensional accuracy.
3. Requirements for fine cutting die
Because the cutting conditions and material separation of fine cutting are very different from those of ordinary cutting, there are certain requirements for dies.
1) The fine cutting pressure is large and the gap between the male and female dies is small. During die fabrication and assembly, the gap must be evenly distributed and maintained neutral.
At the same time, make sure that the die base is accurate, the orientation is accurate and reliable, and the fitting clearance of each sliding part is 0.002 ~ 0.005mm.
2) The main parts of the mold must have sufficient strength and rigidity and high mutual matching accuracy.
The workpiece has high wear resistance and elastic deformation during work is not allowed.
3) Strictly control the depth of the punch entering the die (generally controlled between 0.025 ~ 0.05mm) to avoid damaging the cutting edge.
4) Properly consider the mold exhaust design, pay attention to the lubrication of the working part of the mold, and extend the service life of the mold.
4. Thin filling materials
The fine cutting process is not only a shearing process, but also includes plastic flow and composite metal shearing process, so it is necessary for the fine cutting material to have good plasticity.
That is, the material must have a low yield strength ratio (σs/σb) materials with high elongation and good microstructure (good dispersion), which meet the above requirements, have large deformation capacity due to early initial plastic deformation under low load, so as not to tear during fine cutting.
About 95% of fine-cut parts are steel parts.
For carbon content less than 35%, the tensile strength σb is 300 ~ 600MPa carbon steel, because the ferrite contained therein has good plasticity, can achieve satisfactory fine suppression effect.
Such as carbon steel and its alloy steel with a carbon content of 0.35%～0.7%, or even more, if the cutting edge of the male and female dies encounters pearlite flakes that are not easy to deform, the section will be torn, the quality of the section will be reduced, and die wear will be caused.
Therefore, it is necessary to adopt appropriate heat treatment so that the cementite becomes spherical and evenly distributed in the fine-grained ferrite.
In the blanking process, cementite particles can be squeezed into the soft ferrite matrix, so as to avoid the cutting edge and prevent tensile cracking.
Carbon steel and chrome steel after spheroidization annealing are suitable for fine cutting.
Except lead brass, most non-ferrous metals and alloys can be suitable for fine cutting.
