Design de punção e estampagem: princípios essenciais

Punch and Stamping Design: Essential Principles

The quality of the mold product is directly affected by the quality of the punch. So how important is the punch? Let us share it with you below.

Punch Structure Theory

There are various shapes of punches in the mold. The structure of non-circular section punches should be determined according to the strip process and the state of mold products.

As for circular section punches, there are corresponding national standards.

1. Structure of circular punches

The most common circular punch structures are as follows:

common circular punch structures

We can understand circular punches as A punches and T punches. Punches are divided into first order, second order and third order. This is their difference.

A punches are used in smaller punch positions while T punches are used in larger punch positions.

In another situation, when the thickness of the stamping material and the opening are similar to the structure of the small punch, a protective cover structure is used to improve its longitudinal bending resistance, as shown in the figure.

The figure below shows the structural style used to ensure convenient installation and self-strength when there is space in the punch or when the mold parts are large.

2. Non-circular punch shapes

We need to use technology to shape non-circular punches, but we can understand them as two categories: circular and square. When the part is circular, we can make the fixed part of the punch cylindrical. In the same way, we can make the fixed part of the square.

Normally, using saddle nails to deal with the rotation persuasion of the convex machine can reduce the complexity of making the punch, as shown in the figure below.

However, when using non-cylindrical fixed cylindrical punches, attention must be paid to the displacement of the punch.

3. Puncture fixation methods

Generally, we use a clamping plate to fix the punch, and use clearance to deal with the gap between the punch and the clamping plate.

The gap can be adjusted accordingly based on the material thickness and mold accuracy, generally within 0.01mm on one side.

In the case of a larger diameter, the punch can be made in the form of an assembly step. Multi-head punching dies and other small and medium-sized convex dies are generally fixed in the form of rivets, especially when the distance between them is relatively small.

If the multi-head punching die is designed with a stepped structure, they will interfere with each other and the rivet structure will be more compact in this case.

For clamping large stamped parts, it is a good idea to clamp the upper base of the die and the punch, and make the punch a detachable socket. For some punches that wear out easily and some small punches, the solution is to use a form of replaceable punch attachment.

This structural form has the advantages of reducing mold repair time, speeding up replacement and eliminating the need to disassemble the upper die as a whole. There is also an adhesive attachment method that is not commonly used today and will not be described in detail. See the figure below for details:

4. How to determine the punch length ?

The punch length is generally determined by the mold structure and theoretically determined by the thickness of the mold top plate.

Generally, the shorter the time to meet structure and usage requirements, the better. The punch length can be calculated by the following formula:

L = h1 + h2 + h3 + (10-20) (mm)

Where h1 is the thickness of the guide ruler (mm), h2 is the thickness of the discharge plate (mm), h3 is the thickness of the convex mold fixing plate (mm).

The length of the punch is mainly determined by the structure of the punching die.

Conceptually, it is determined by the thickness of the mold's top plate. Generally, the shorter the better when structure and usage requirements are reasonable. The above formula can be used to calculate the length of the convex mold.

The formula of 10-20 millimeters includes the punch entry depth, the punch repair amount, and the distance between the punch discharge plate and the punch fixing plate in the closed state.

The length of the punch should be modified according to the structure and requirements of the punching die. It is only necessary to check when the punch section is very small and the thickness and hardness of the punched material are large.

Otherwise, in general situations, it is not necessary to calculate the punch hardness.

Based on the analysis above, it's clear that punches matter. Therefore, designers should pay more attention to them in their designs.

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