Let us first take a look at the main factors affecting the stability of metal stamping parts, namely: the use of mold materials; the strength requirements of mold structural parts; the stability of stamping material properties; the fluctuation characteristics of material thickness; the range of material changes; The resistance of the tensile rib; the variation range of the blank holder force; the choice of lubricant.

   What is stability? Stability is divided into process stability and production stability. Process stability refers to a process plan that satisfies the stability of producing qualified products; production stability refers to a stable production capacity in the production process.

    Since most of the domestic mold manufacturing enterprises are small and medium-sized enterprises, and a considerable number of them are still in the traditional workshop-style production management stage, the stability of the mold is often ignored, resulting in a long mold development cycle and high manufacturing costs. Restricted the pace of development of the enterprise.

    Let us first take a look at the main factors affecting the stability of metal stamping parts, namely: the use of mold materials; the strength requirements of mold structural parts; the stability of stamping material properties; the fluctuation characteristics of material thickness; the range of material changes; The resistance of the tensile rib; the variation range of the blank holder force; the choice of lubricant.

    As we all know, the metal materials used in stamping dies involve many types. Due to the different roles of various parts in the die, the requirements and selection principles for their materials are also different. Therefore, how to choose mold materials reasonably has become one of the most important tasks in mold design.

    When selecting mold materials, in addition to requiring the materials to have high strength, high wear resistance and appropriate toughness, the characteristics and output requirements of the processed product materials must also be fully considered, so as to achieve the stability requirements of mold forming.

    In actual operation, because mold designers tend to choose mold materials based on personal experience, in metal stamping, the problem of unstable mold formation caused by improper selection of mold parts materials often occurs. The following examples illustrate

   [Example] On an iron plate with a material thickness of 1.2mm (shear strength 64kgf/mm2), a circular hole with a diameter of 2.8mm is machined.

 ① Punching shear force: P=Ltτ. in,

 L: Blanking profile length (mm);

 t: the thickness of the material (mm);

τ: shear strength of material (kgf/mm2); d: punch diameter (mm); P=3.14×2.8×1.2×64=675kgf

② Stress of punch edge: σS=4tτ/d. That is,

σS=4×1.2×64/2.8=110kgf/mm2

   As shown in the figure above: when σS is 110kgf/mm2, the punch material is SKD11, and the number of punches reaches about 9000 punches, the punch edge may be damaged. If the material is replaced with SKH51, the number of strokes can be increased to about 40,000 strokes. It can be seen that in the mold design stage, it is necessary to carry out the necessary strength check calculation for the mold structural parts, and the following precautions should be taken when selecting materials:

① Stress on punch < allowable compressive stress of punch material

②In order to improve the bending strength of the punch, a material with a large elastic coefficient should be selected

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

   It is worth noting that in the process of metal stamping, since each stamped sheet has its own chemical composition, mechanical properties and characteristic values closely related to stamping performance, the performance of stamping materials is unstable, the thickness of stamping materials fluctuates, and The change of stamping material not only directly affects the precision and quality of metal stamping, but also may cause damage to the mold.

   Taking stretch rib as an example, it occupies a very important position in metal stamping. In the process of stretch forming, the forming of the product needs to have a certain amount of tensile force that is appropriately distributed along the fixed periphery. This tensile force comes from the force of the stamping equipment, the deformation resistance of the edge material, and the flow resistance on the blank holder ring. . The generation of flow resistance, if only rely on the blank holder force, the friction between the mold and the material is not enough.

   To this end, a tensile rib that can generate greater resistance must be set on the blank holder to increase the resistance of the feed, so that the material can produce greater plastic deformation to meet the requirements of plastic deformation and plastic flow of the material. At the same time, by changing the size and distribution of the resistance of the stretching rib, and controlling the speed and feed amount of the material flowing into the mold, the effective adjustment of the tensile force and its distribution in each deformation area of the stretched part is realized, thereby preventing stretching Quality problems such as cracking, wrinkling, and deformation of the product during 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 considered, and the stretching rib should be arranged according to the variation range of the blank holder force and the form of the stretching rib should be determined, so that each deformation area can be deformed according to the needs. The way and degree of deformation complete the forming.

In order to solve the problem of die stability of metal stamping parts, it is necessary to strictly check the following aspects:

   ①In the process formulation stage, by analyzing the product, predict the possible defects of the product in the manufacture, so as to formulate a stable manufacturing process plan;

   ② Implement the standardization of the production process and the standardization of the production process;

   ③ Establish a database, and continuously summarize and optimize it; with the help of CAE analysis software system, get the optimal solution.