In the design and manufacture of molds, designers' experience and skills play a key role. Whether the design is reasonable or not can be confirmed through trial moulds; the moulds can be finalized through multiple trials and repeated modifications. In production practice, once molds are put into use on the production line, they often cause various problems, fail to meet the production requirements or technical requirements of the products, cause abnormal shutdown of the production line, and cause many unstable factors. Therefore, how to improve the stability of the mold has become a practical problem facing mold manufacturers.
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Die and stamping stability and its influencing factors
What is stability? Stability is divided into process stability and production stability. Process stability refers to a process scheme that satisfies the stability of a production-qualified product; production stability refers to a production capacity that is stable in the production process.
As most of the domestic mold manufacturing enterprises are small and medium-sized enterprises, and a considerable part of these enterprises still remain in the traditional workshop-style production management stage, they often overlook the stability of the mold, resulting in long mold development cycle, high manufacturing costs, serious Restricted the pace of development of enterprises.
Let us first look at the main factors that affect the stability of the mold and press forming, namely: the use of mold materials; strength requirements of the mold structure parts; stability of stamping material properties; fluctuation characteristics of the material thickness; ; The resistance of the tensile ribs; the range of blank holder force; the choice of lubricant.
How to choose the right materials and examples
As we all know, the metal materials used in stamping molds involve many types. Due to the different roles of various parts in molds, the requirements and selection principles for their materials are also not the same. Therefore, how to reasonably select mold materials becomes one of the most important tasks in mold design.
When selecting mold materials, in addition to requiring high strength, high wear resistance, and appropriate toughness, the materials must also take full account of the characteristics of the material being processed and the output requirements, so as to achieve the stability requirements of mold forming.
In actual operation, the mold designer tends to select mold materials based on personal experience. In the press forming, there often arises a problem that the molding of the mold parts is not stable due to improper selection of the material of the mold parts. The following examples illustrate.
[Example] A circular hole with a diameter of 2.8 mm was machined on an iron plate with a material thickness of 1.2 mm (shear strength of 64 kgf/mm2).
1 Shearing force: P = Ltτ. among them,
L: punching profile length (mm);
t: thickness of the material (mm);
τ: shear strength of the material (kgf/mm2); d: punch diameter (mm); P = 3.14 × 2.8 × 1.2 × 64 = 675 kgf
2 The stress of the punch edge: σS=4tτ/d. That is,
σS=4×1.2×64/2.8=110kgf/mm2 
Figure Tool Steel Fatigue Characteristics
1 Punch withstand stress < Allowable compressive stress of punch material
2 In order to improve the flexural strength of the punch, a material with a large elastic coefficient should be used.
3 According to Euler's formula, check the stability ability
Comprehensively weighing various factors that affect stability
It is worth noting that in the stamping process, since each stamped sheet has its own chemical composition, mechanical properties and characteristic values ​​closely related to the stamping performance, the properties of the stamping material are unstable, the thickness of the stamping material fluctuates, and The change of the stamping material not only directly affects the precision and quality of the press forming process, but also may cause damage to the mold.
Taking tensile ribs as an example, it occupies a very important position in the stamping process. In the stretch forming process, the formation of the product requires a tensile force of a certain size and distributed along the fixed periphery. The tensile force comes from the force of the stamping device, the deformation resistance of the material of the edge portion, and the flow resistance on the blank bead surface. . The flow resistance, if only relying on the role of blank holder force, the friction between the mold and the material is not enough.
For this reason, it is necessary to set tensile ribs on the blank holder ring to increase the resistance, so as to increase the resistance of the feed material, so that the material has a greater plastic deformation, so as 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 tensile ribs, and controlling the speed and amount of material flowing into the die, an effective adjustment of the pull force and its distribution in the deformation regions of the tensile members can be achieved, thereby preventing stretching. Cracking, wrinkling, and distortion of the product during molding. From the above, we can see that in the development of the stamping process and mold design process, we must consider the size of the tensile resistance, according to the range of the blankholder force to arrange the tensile ribs and determine the form of tensile ribs, so that the deformation of the deformation zone as needed The way and degree of deformation are completed.
If you make a summary, in order to solve the problem of mold stability, you need to strictly control the following aspects:
1 In the process of process formulation, through the analysis of the product, predict the possible defects in the manufacture of the product, thereby formulating a stable manufacturing process plan;
2 to implement the standardization of production processes and the standardization of production processes;
3 establish a database, and continue to summarize its optimization; with CAE analysis software system, the optimal solution.