Die is the key process equipment for stamping production. With the continuous development of mold industry, molds are more and more widely used in weapons industry, machinery industry and the production of daily necessities. China's mold industry has entered a period of rapid development, but compared with developed countries in the world, there is still a big gap in mold manufacturing level and performance.
More than 90% body-in-white parts of modern automobiles are mass-produced by stamping dies.
According to the service life requirements of automobile cold stamping die, 500,000 qualified parts can be produced in multiple batches and small batches under normal use and maintenance. Therefore, the performance and quality of die materials have a great influence on the service life of the die. Therefore, the research and development of die materials have been highly valued by die steel manufacturers and developed rapidly.
1. Present situation of mold materials
In recent years, the production technology of die steel in China has developed rapidly, and the materials used to manufacture cold stamping dies are mainly divided into the following categories:
(1) high-carbon low-alloy cold-working die steels, such as 9SiCr, 7CrSiMnMoV, 8Cr2MnWMoVS, etc.
(2) Wear-resistant cold-working die steels, such as: 6Cr4W3Mo2VNb, Cr 12, Cr 12MoV, Cr1v1etc.
(3) Impact-resistant cold-working die steels, such as 4CrW2Si, 5CrW2Si, 6CrW2Si, etc.
(4) High-speed steel for cold working dies, such as: W6Mo5Cr4V2, W12Mo3Cr43N, W9Mo3Cr4V, etc.
2. The performance of automobile mold materials
(1) Requirements for the use of blanking die materials
The material of the thin plate blanking die requires high wear resistance and hardness, and the thick plate blanking die requires high wear resistance and compression yield point, as well as high fracture resistance and toughness to prevent the die from breaking or edge collapse.
(2) Requirements for using drawing and forming die materials
It is required that the materials of the working parts of the mold have high wear resistance and hardness, certain strength and toughness, good machinability, good adhesion resistance (bite resistance) and small deformation during heat treatment.
According to the present situation of stamping die in automobile factory, the main materials used in automobile die are: Mo-Cr cast iron, Cr 12MoV and as-cast air-cooled steel.
Molybdenum-chromium cast iron: a kind of high chromium white cast iron belonging to nickel hard white cast iron system. Because its crystal structure is composed of M7C3 carbide and other austenite transformations, its matrix can show high wear resistance after annealing into martensite. At the same time, chromium contained in it can significantly improve strength, hardness and wear resistance, manganese can significantly improve toughness, and molybdenum can refine steel grains and improve hardenability. The heat treatment method is surface quenching, which saves a lot of heat treatment time. The hardness after quenching is HRC50.