模具的历史发展英文文献和中文翻译(3)
Due to the characteristics of stamping deformation and mechanics mentioned above，the stamping technique is different from the bulk metal forming：
(1) The importance of the strength and rigidity of the die in stamping forming is less than that in bulk forming because the blank can be formed without applying large pressure unit area on its surface．Instead，the techniques of the simple die and the pneumatic and hydraulic forming are developed.
(2) Due to the plane stress or simple strain state in comparison with bulk forming，more research on deformation or force and power parameters has been done, stamping forming can be performed by more reasonable scientific methods．Based on the real time measurement and analysis on the sheet metal properties and stamping parameters, by means of computer and some modem testing apparatus research on the intellectualized control of stamping process is also in proceeding.
(3) It is shown that there is a close relationship between stamping forming and raw material. The research on the properties of the stamping forming，that is，forming ability and shape stability, has become a key point in stamping technology. The research on the properties of the sheet metal stamping not only meets the need of the stamping technology development，but also enhances the manufacturing technique of iron and steel industry, and provides a reliable foundation for increasing sheet metal quality．
3 China's mold industry and its development trend
Due to historical reasons for the formation of closed, "big and complete" enterprise features, most enterprises in China are equipped with mold workshop, in factory matching status since the late 70s have a mold the concept of industrialization and specialization of production. Mold production industry is small and scattered, cross-industry, capital-intensive, professional, commercial and technical management level are relatively low.
According to incomplete statistics, there are now specialized in manufacturing mold, the product supporting mold factory workshop (factory) near 17 000, about 600 000 employees, annual output value reached 20 billion yuan mold. However, the existing capacity of the mold and die industry can only meet the demand of 60%, still can not meet the needs of national economic development. At present, the domestic needs of large, sophisticated, complex and long life of the mold also rely mainly on imports. According to customs statistics, in 1997 630 million U.S. dollars worth of imports mold, not including the import of mold together with the equipment; in 1997 only 78 million U.S. dollars export mold. At present the technological level of China Die & Mould Industry and manufacturing capacity, China's national economy in the weak links and bottlenecks constraining sustainable economic development.
3.1 Research on the Structure of industrial products mold
In accordance with the pision of China Mould Industry Association, China mold is pided into 10 basic categories, which, stamping die and plastic molding two categories accounted for the main part. Calculated by output, present, China accounts for about 50% die stamping, plastic molding die about 20%, Wire Drawing Die (Tool) about 10% of the world's advanced industrial countries and regions, the proportion of plastic forming die die general of the total output value 40%.
Most of our stamping die mold for the simple, single-process mode and meet the molds, precision die, precision multi-position progressive die is also one of the few, die less than 100 million times the average life of the mold reached 100 million times the maximum life of more than accuracy 3 ~ 5um, more than 50 progressive station, and the international life of the die 600 million times the highest average life of the die 50 million times compared to the mid 80s at the international advanced level.
China's plastic molding mold design, production technology started relatively late, the overall level of low. Currently a single cavity, a simple mold cavity 70%, and still dominant. A sophisticated multi-cavity mold plastic injection mold, plastic injection mold has been able to multi-color preliminary design and manufacturing. Mould is about 80 million times the average life span is about, the main difference is the large deformation of mold components, excess burr side of a large, poor surface quality, erosion and corrosion serious mold cavity, the mold cavity exhaust poor and vulnerable such as, injection mold 5um accuracy has reached below the highest life expectancy has exceeded 20 million times, the number has more than 100 chamber cavity, reaching the mid 80s to early 90s the international advanced level.