punch structure theory
There are many types of punches in the mold. The structure of the punch with a non-circular cross-section should be determined according to the process of the strip and the state of the mold product. For the punch with a circular cross-section, the country has corresponding standards.
1. The structure of the circular punch
The known common circular punch structures are as follows
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We can understand round punches as A punches and T punches. Punches are divided into first-order, second-order and third-order. This is their difference. A punch is used for smaller punching positions, and T punch is used for larger punching positions. In another case, when the thickness and hole diameter of the stamping material are similar to the structure of the small hole punch, the protective cover structure is used to improve its longitudinal bending resistance, as shown in the figure
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The figure below shows the structural style used in order to ensure its convenient installation and self-strength when there is space for punching or the mold parts are large.
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2. Non-circular punch shape
We need to shape non-circular punches by technology, but we can understand them as two types of round and square. When the workpiece is round, we can make the fixed part of the punch cylindrical, and similarly, we can also make the fixed part of the punch square. Usually, a seam pin is used to deal with the rotation of the convex machine. This method as shown in the figure below can reduce the complexity of making the punch, but the non-cylindrical punch fixed with a cylindrical shape should pay attention to the movement of the punch.
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3. The way to fix the punch
Generally, we use a splint to fix the punch, and use a clearance fit to deal with the gap between the punch and the splint. The gap can be properly scheduled through the thickness of the material and the precision of the mold, generally 0.01mm on one side.
In the case of larger diameters, punches can be made in the form of assembly steps. Some small and medium-sized punches such as multi-head punches are usually fixed in the form of riveting heads, especially when the distance between each other is relatively small, if the multi-head punching dies use a stepped structure, they will interfere with each other, and the riveting head structure will be more compact at this time.
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For the fixing of punching large workpieces, we can fix the upper die base and the punch, and it is a good way to make the punch as an insert for quick release. Some punches are easy to wear and some small punches can be solved with replaceable punch fixing forms.
To achieve better reduction of mold repair time, faster replacement, and no need to disassemble the upper mold as a whole, this is the advantage of this structural form. There is also a method of glue filling and fixing that is not used very much now, so I will not describe it in detail, as shown in the following figure:
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4. How to determine the punch length
The length of the punch is generally determined by the structure of the mold, and theoretically determined by the thickness of the upper mold template. In general, the shorter the time before the structural and operational requirements are met, the better. The punch length can be calculated according to the following formula:
L = h1 + h2 + h3 + (10~20) (mm)
h1 is the thickness of the guide bar (mm)
h2 is the thickness of stripping plate (mm)
h3 is the thickness of the punch fixed plate (mm)
The punch is mostly determined by the structure of the die to be punched. Conceptually, it is determined by the thickness of the upper template. When the structure and use requirements are reasonable, the shorter the better, the above formula can be used to calculate the length of the punch.
The above formula of 10~20 mm includes the depth of punch entry, the modulus of punch, and the distance between the stripper plate and the punch clamping plate in the die in the closed state. The length of the punch should be modified according to the die structure and requirements. It is necessary to perform calibration only when the section of the punch is small and the thickness and hardness of the punched material are large. Otherwise, in fact, the strength and hardness of the punch should not be calculated under normal circumstances.
