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The proportion of fine blanking in industrial production is increasing, so the requirements for molds are getting higher and higher. How to extend the life of the mold, reduce wear, reduce costs, and increase economic benefits are the most concerning issues for manufacturers. There are many factors that affect the life of the mold. Wear is the most important factor affecting the life of the mold. Today, we will further analyze and discuss the wear mechanism and protection of the decay.
Features of Fine Blanking Technology
The fine blanking technology adopts the acceptable gap, the ring gear plate, and the top plate in the die to play the role of the reverse die so that the stamping parts can obtain higher dimensional accuracy and surface roughness. In some industrially developed countries, the machining accuracy of the mold industry has reached the micron level, which can replace cutting under certain conditions.
Fine blanking technology has the following advantages:
- The dimensional accuracy of fine punching parts can reach the IT7~IT8 level, and the surface roughness of the shear section is Ra 2. 4~0. 4μm, with high perpendicularity and parallelism;
- Compared with cutting, fine blanking technology can generally improve work efficiency by 10 times;
- It can save a lot of electric energy consumed by cutting machine tools and cutting processing. The surface of the workpiece after fine blanking is work hardened, and the subsequent quenching process can be canceled;
- The fine-blanking composite process can be used to simplify the forming process, and it can be combined with other forming processes such as bending, extrusion, embossing, etc. for composite or progressive stamping. The parts produced to account for more than 20% of all fine blanking parts.
The Mechanism of Fine Blanking Technology
The fine punching process adds rounded corners to the die edge, reduces the gap between the concave and punch die, and adds a ring gear pressure plate and an ejector. In order to inhibit the tearing of the material before punching and ensure the smooth progress of plastic deformation, the metal material needs to be subjected to static pressure in the punching deformation area, and the material is in a state of three-way compressive stress (punching force, blank holder force, and back pressure), which is a precise A necessary condition for rushing. During fine blanking, the blank holder presses the material to prevent the material outside the shear deformation zone from flowing with the punch during the shearing process. The support function of the blank holder and the counter pressure plate, coupled with the small gap between the convex and concave dies (usually 0.5% of the material thickness, 1/10 of the ordinary punching), make the workpiece tightly pressed and prevent the parts from being damaged.
Warpage creates tensile stress, leading to brittle fracture, which constitutes a ductile material shear condition. If necessary, the three-way compressive stress tensor in the deformation zone can be increased to improve the plasticity of the material. The punching punch and the die edge of the blanking die can be rounded to reduce the stress concentration at the edge and avoid cracks. , to improve the stress state of the deformation zone, and obtain bright blanking vertical sections and blanking parts with small slope, smooth surface, and high dimensional accuracy.
Of course, the fine blanking process is required to achieve the required purpose. In addition to the plastic shear deformation caused by the special structure of the working part of the fine blanking die, there are also three-way pressures such as pressing, punching and reverse topping, and these three pressures are required to be pressed. Sequential pressure. Therefore, precision blanking with a ring gear platen requires a triple-action die and press with three pressures, as well as a push-piece and unloading action after the sheet is separated. There are also certain requirements for fine blanking materials, lubrication, and fine blanking mechanism. Only when the above sufficient conditions are met can the purpose of fine blanking be achieved.
Requirements For Fine Punching Dies
Since the blanking conditions and material separation of fine blanking are very different from ordinary blanking, there are certain requirements for the mold.
- The fine blanking pressure is large, and the gap between the convex and concave dies is small. During the manufacture and assembly of the mold, the gap must be evenly distributed and maintained neutrality. 0. 002 ~ 0. 005 mm.
- The main parts of the mold must have sufficient strength and rigidity, and the mutual matching precision is high. The working part has high wear resistance, and elastic deformation is not allowed when working.
- Strictly control the depth of the punch entering the concave die (generally controlled at 0. 025 ~ 0. 05 mm) to avoid damage to the cutting edge.
- Properly consider the exhaust design of the mold, pay attention to the lubrication of the working part of the mold, and prolong the life of the mold.
Fine Punching Material
The fine blanking process is not only a shear process but also includes the plastic flow and shear composite process of the metal, so the fine punching material must have good plasticity, that is, the material should have a lower yield ratio (σs /σb ), High elongation and good structure (good dispersion), the material that meets the above requirements, the early initial plastic deformation under the action of low load, has a large deformation capacity, so that the phenomenon of tearing will not occur during the fine blanking process.
About 95% of the fine-blanking parts are steel parts. For carbon steel with a carbon content of less than 35% and a tensile strength σb of 300-600MPa, due to the good plasticity of the ferrite, satisfactory fine-blanking effects can be obtained. Because the carbon content is between 0.35% and 0.7%, or even higher than carbon steel and its alloy steel, if the edges of the convex and concave die to encounter the pearlite flakes that are not easily deformed, the section will be torn and the section will be torn. The quality declines, which causes the wear of the mold, so it is necessary to use appropriate heat treatment to make the cementite spherical and small particles, which are evenly distributed in the fine-grained ferrite.
During the punching process, the cementite particles can be squeezed into the soft ferrite matrix, so as to avoid the cutting edge and prevent cracking. Carbon steel and chrome steel after annealing are suitable for fine blanking. Except for lead brass, most non-ferrous metals and alloys can be used for fine blanking.