First, let's take a look at the main factors affecting the stability of metal stamping parts, respectively: the use of mold materials; The strength requirements of mold structural parts; Stability of stamping material properties; Fluctuation characteristics of material thickness; The range of material variation; Tensile reinforcement resistance; Variation range of blank holder force; Choice of lubricant.

 

The stability of metal stamping parts production and its influencing factors

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What is stability? Stability is divided into process stability and production stability. Process stability refers to the process scheme that satisfies the stability of qualified products; Production stability refers to the production capacity with stability in the production process.

 

Because most of the domestic mold manufacturing enterprises are small and medium-sized enterprises, and a considerable part of them, still stay in the traditional workshop production management stage, often ignore the stability of the mold, resulting in the mold development cycle long, high manufacturing costs, seriously restrict the pace of enterprise development.

Metal stamping parts

First, let's take a look at the main factors affecting the stability of metal stamping parts, respectively: the use of mold materials; The strength requirements of mold structural parts; Stability of stamping material properties; Fluctuation characteristics of material thickness; The range of material variation; Tensile reinforcement resistance; Variation range of blank holder force; Choice of lubricant.

 

As is known to all, the metal materials used in stamping die involve many kinds. Because of the different roles played by various parts in the die, the requirements and selection principles of its materials are not the same. Therefore, how to choose the mould material reasonably becomes one of the most important work in mould design.

 

The selection of die materials, in addition to the requirements of materials must have high strength, high wear resistance and appropriate toughness, but also must fully consider the characteristics of the product materials and production requirements, so as to achieve the stability of the mold forming requirements.

Metal stamping parts

But in the actual operation, because the mold designer tends to choose the mold material according to the personal experience, in the metal stamping will often appear because of the improper selection of the material of the mold parts and lead to the forming of the unstable problem. Here are some examples

A circular hole with a diameter of 2.8mm is machined on an iron plate with a thickness of 1.2mm (shear strength of 64kgf/mm2).

Impulse shear force: P=Lt. Among them,

L: Length of blanking contour (mm);

T: Thickness of the material (mm);

: The shear strength of the materials (KGF /mm2); D: Punch diameter (mm); P = 3.14 x 2.8 x 1.2 x 64 = 675 KGF

Stress on the cutting edge of punch: S=4t /d. That is,

Sigma S = 4 x 1.2 x = 110 KGF/was 64/2.8

 

Metal stamping parts

As shown in the figure above, when the S is 110kgf/mm2, the punch material is SKD11, and the punch stroke is about 9000, the punch edge may be damaged. If the material is changed to SKH51, the impulse is expected to increase to about 40,000 impulse. It can be seen that, in the mold design stage, it is necessary to carry out the necessary strength checking calculation of the mold structure, and the selection of materials have the following precautions:

(1) The stress borne by the punch < the allowable compressive stress of the punch material

(2) in order to improve the bending strength of punch, should choose the material with large elasticity coefficient

(3) According to Euler's formula, the stability of the ability to check.

 

It is important to note that in the process of metal stamping, because each kind of pressing plate has its own chemical composition, mechanical properties and is closely related to the stamping performance characteristic value, stamping material performance is not stable, punching material thickness fluctuation, and the change of the stamping material, not only directly affect the metal stamping processing precision and quality, also may cause the damage of the mould.

 

Take stretch bar as an example, it occupies a very important position in metal stamping. In the process of drawing forming, the forming of the product needs to have a certain size, and the appropriate distribution of tension along the fixed periphery, this tension is due to the pressing force of the equipment, the deformation resistance of the edge part of the material, and the flow resistance on the blank holder surface. However, if the flow resistance only depends on the blank holder force, the friction between the mold and the material is not enough.

 

In order to meet the requirements of plastic deformation and plastic flow of the material, it is necessary to set a stretch bar on the blank holder that can produce greater resistance to increase the resistance of the feed. At the same time, by changing the size and distribution of tensile reinforcement resistance, and controlling the flow speed and feed amount of materials into the die, the tension and its distribution in each deformation area of the stretch parts can be effectively adjusted, so as to prevent the product from cracking, wrinkling, deformation and other quality problems during the stretch forming. It can be seen from the above that in the process of formulating stamping process and die design, the size of tensile resistance must be taken into account, and the form of tensile reinforcement should be arranged according to the variation range of blank holder force so that each deformation area can be formed according to the required deformation mode and degree of deformation.

 

Metal stamping parts

In order to solve the metal stamping die stability problem, we need to strictly check the following aspects:

 

(1) In the process formulation stage, through the analysis of the product, predict the product in the manufacture of possible defects, so as to develop a stable manufacturing process plan;

(2) to implement the standardization of the production process, the standardization of the production process;

(3) To establish a database, and constantly optimize its summary; With the help of CAE analysis software system, the optimal solution is obtained.