Designer experience and skills play a key role in the design and manufacture of molds. Whether the design is reasonable or not can be confirmed by trial mode; and the mold needs to be tried and modified repeatedly to complete it. In the production practice, once some molds are put into the production line, they often have various problems, which can not meet the production requirements or technical requirements of the products, resulting in abnormal shutdown of the production line, which brings many unstable factors. Therefore, how to improve the stability of the mold has become a practical problem faced by mold manufacturing enterprises.
Stability of mold and stamping and its influencing factors
What is stability? Stability is divided into process stability and production stability. Process stability refers to a process plan that satisfies the stability of a qualified product; production stability refers to a production capacity with stability during the production process.
Since most domestic mold manufacturing enterprises are small and medium-sized enterprises, and quite a few of them are still in the traditional production management stage, they often neglect the stability of the mold, resulting in long mold development cycle and high manufacturing cost. It has restricted the pace of development of enterprises.
Let us first look at the main factors affecting the stability of the mold and stamping, namely: the use of mold materials; the strength requirements of the mold structural parts; the stability of the properties of the stamping materials; the fluctuation characteristics of the material thickness; the range of material changes The resistance of the tensile ribs; the range of the blanking force; the choice of lubricant.
How to choose materials and examples correctly
As is well known, the metal materials used in stamping dies involve many types. Due to the different functions of various parts in the mold, the requirements and selection principles of the materials are not the same. Therefore, how to properly select the mold material has become one of the most important tasks in mold design.
When selecting the mold material, in addition to the requirement that the material must have high strength, high wear resistance and appropriate toughness, the characteristics and production requirements of the material to be processed must be fully considered, so as to achieve the stability requirements of the mold forming.
In actual operation, since the mold designer tends to select the mold material based on personal experience, the problem of unstable mold formation due to improper selection of the material of the mold part often occurs in the press forming. The following is an example.
[Example] A circular hole having a diameter of 2.8 mm was machined on an iron plate having a material thickness of 1.2 mm (shear strength of 64 kgf/mm2).
1 punching force: P = Ltτ. among them,
L: blanking 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=675kgf
2 Stress of the punch edge: σS=4tτ/d. That is,
σS=4×1.2×64/2.8=110kgf/mm2
Fatigue properties of tool steel
As shown in the figure above, when the σS is 110kgf/mm2, the punch material is SKD11, and the punch reaches about 9000 punches, the punch edge may be damaged. If the material is replaced by SKH51, it is expected to increase the level 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 are taken when selecting materials:
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