Types and application status of plastic die steel

2022-08-15
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Types and application status of stamping die/plastic die steel

1 Introduction with the rapid development of China's plastic industry, the demand is also growing, and higher and higher requirements are put forward for plastic molds. This has promoted the continuous development of plastic molds. Mold material is the basis of manufacturing mold

at present, plastic molds are developing towards high efficiency, high precision and high service life. Nevertheless, China's mold technology and mold life still lag behind some industrial developed countries. The structure of mold materials and heat-treated plastic mold is complex, and the requirements for plastic mold size accuracy and surface roughness are very high, and the requirements for plastic mold cavity materials are relatively stringent. Therefore, the correct selection of mold materials and their heat treatment methods is very important for improving mold quality and prolonging mold service life

2. The performance requirements of plastic molds. The components of plastic molds can be divided into two categories according to their uses. One category is structural parts, including gating system, guide parts, fixed (moving) formwork, ejector mechanism parts, support parts, etc. the materials used are generally medium and low carbon carbon structural steel or alloy. The other is formed parts. Including cavity, core, inlay, etc., which are the key parts of directly molded plastic parts. The working temperature of plastic mold is 200-300 ℃. The plastic mold cavity is complex, and the requirements for dimensional accuracy and surface roughness are high. The corresponding requirements are put forward for the machinability, mirror polishing and grinding performance, heat treatment deformation and dimensional stability of plastic mold steel. Therefore, when selecting mold materials, we should ensure the performance requirements of the mold and improve its processing performance as much as possible Its selection principle mainly includes the following points:

1) it has certain comprehensive mechanical properties Formed parts should bear temperature, pressure, erosion and wear in the working process, so they are required to have certain strength, plasticity and toughness. (2) The surface of the mold cavity should have a sufficiently thick hardened layer with a certain hardness and wear resistance. (3) Good machinability. The shape of plastic mold is often complex, and the cutting cost often accounts for the vast majority of the mold (generally about 75%), so it is required to have good machinability. (4) Select according to the size and accuracy requirements of plastic parts For large and high-precision injection molds, when plastic parts are produced in large quantities, pre hardened steel is used to prevent heat treatment deformation

3. The type of plastic mold steel

there have been many books and materials on the performance of traditional common mold steel in China. This paper mainly introduces the plastic mold steel developed in China in recent years and introduced from abroad, which has been (or will be) popularized in production

3.1 pre hardened plastic mold steel

this kind of steel is made by adding appropriate elements such as chromium, manganese and nickel on the basis of carbon. Generally, it is made into modules after full forging, and is pre heat treated to the required hardness for the user to make molds. When the hardness is 30 to 40HRC, turning, drilling, milling, engraving, fine filing and other processing can be directly carried out. After finishing, it can be directly delivered for use without heat treatment, so as to ensure the manufacturing accuracy of the mold. After finishing, it can be directly delivered for use, which completely avoids the influence of heat treatment deformation, thus ensuring the manufacturing accuracy of the mold At the same time, it also has high wear resistance, ultra-high polishing and pattern etching, which is commonly used in oversize, complex and long-life plastic molds. Pre hardened plastic mold steel mainly includes P20, P20s, p20bs steel, etc. P20 steel has good hardenability and certain toughness, and can be carburized, nitrided or carbonitriding. After carburizing and quenching, the surface hardness can reach 65hrc, with high thermal hardness and wear resistance

3.2 free cutting plastic mold steel

free cutting steel is to add free cutting elements on the basis of pre hardened steel to overcome the difficulties of difficult cutting Add free cutting elements s, B and ca. Foreign free cutting pre hardened steel is mainly S-Series, but there are also s-se series, but the price of se is relatively expensive. S-Series free cutting steel has good machinability under low and medium speed cutting conditions, but MNS extending along the deformation direction after thermal deformation increases toughness, and sulfide segregation is more serious when the section increases. China has developed some sulfur-containing free cutting pre hardened plastic mold steels, such as 8Cr2MnWMoVS and S-Ca composite free cutting plastic mold steel scrnimnmovsca (snisca for short). 8cr2.s is a kind of free cutting precision plastic forming die steel, which is developed to meet the urgent need of precision plastic dies and precision punching dies without clearance for thin plates. It is characterized by high carbon content in steel, which is mainly to make the matrix of quenched steel have a certain amount of carbon and retain a certain amount of fine and dispersed residual carbides, which can not only inhibit the growth of austenite grains during quenching and heating, but also ensure that the mold has a certain wear resistance. The purpose of adding CR, W, Mo and V to the steel is to improve the hardenability. Since Erdogan was elected in 2003, he has refined the austenite grains of the impact testing machine of Jinan new era Gold Testing Instrument Co., Ltd. under the conventional manual pendulum impact testing machine to form the use benefits and preparation efficiency of the alloying pressure testing machine. How to ensure the compound and improve the wear resistance of the steel

8Cr2. S steel has simple heat treatment process and good hardenability. It can be heated at 860900 ℃, oil quenched, air quenched or Austempered in 240280 ℃ nitrate. The steel with a diameter of X100 ~ can be quenched thoroughly by air quenching. The hardness after quenching is 62}64hrc, and the tempering hardness when tempering at 550620 ℃ is 40}48hrc

3.3 age hardening plastic steel

age hardening steel has two types, namely maraging steel and low nickel aging steel. Maraging steel contains high nickel and is expensive, which is rarely used in China. 25crni3moa1 is a low nickel aging steel. After 8800c quenching and 6800c-7000c high temperature tempering, the hardness is HRC, which can be machined. After 5200c-5400c aging, the hardness reaches HRC. Aging is strengthened by precipitation of ordered intermetallic compound niai coherent with the matrix

pms steel is a new precipitation hardening plastic die steel, which has good cold and hot workability and comprehensive mechanical properties, simple heat treatment process, small deformation, high hardenability, suitable for surface strengthening treatment, and extrusion forming of die cavity in softening state. The forging can be machined without annealing after air cooling. Adding aluminum to SM2 steel can precipitate hardened phase ni3a1 during aging, adding chromium can improve the hardenability of steel, and adding sulfur and manganese can form free cutting phase mn S. Therefore, SM2 steel has slightly higher hardenability and better cutting performance than PMS steel

4. The development and Prospect of plastic mold steel in China the production technology of mold steel in China has developed rapidly, forming China's own mold steel series. With the adjustment of global industrial structure, traditional industries such as manufacturing industry have become increasingly saturated due to the European and American markets, labor costs have increased year by year, profits have decreased, and the focus has shifted to developing countries Due to the abundant and cheap labor resources, China's mold potential market is large, which determines that China will develop into a mold manufacturing country. In plastic molding and processing, the quality of mold plays an unspeakable role in ensuring product quality. But at the same time, there are still many deficiencies in the production technology and product quality of die steel in China. Many steel products for manufacturing large, precision and long-life molds still need to be imported from abroad, which has become the country with the largest number of imported molds in the world. Looking forward to the future, the following work is urgently needed

4.1 improve the quality of die steel

now many die steel plants in China have adopted advanced metallurgical equipment and processes to produce die steel, but there is still a gap compared with the foreign advanced level, and the output of die steel adopting advanced processes is very small. In order to improve the quality of die steel, steel mills should not only increase the proportion of die steel produced by advanced technology, but also improve management, so as to facilitate the mass production of die steel with high purity, good uniformity and stable quality. Some special steel mills in China have adopted out of furnace refining, vacuum smelting, rapid forging machine and precision forging machine to produce die steel. The quality of die steel has been greatly improved, such as D2, P20, etc., and the quality of exported products can reach the international advanced level. However, electroslag remelting is mostly used for mold steel with high purity requirements in foreign countries, which further improves the purity, density, isotropy and uniformity of steel, and reduces segregation. China still needs to carry out further work in this regard

4.2 promotion and application of new die steels with excellent performance

China has developed new characteristic die steels with excellent performance, which reach or exceed the same level abroad, but the promotion quantity and application scope of these new steels are not large enough. We should selectively develop advanced die steels, such as powder metallurgy die steels, multi-element free cutting plastic die steels, glass and ceramics, The demand and shortage of high-end professional talents related to forming dies such as refractory bricks and floor tiles are bound to be more severe. Steel for tools will be used to improve China's die steel series

with the development of China's mold industry, plastic molds are developing in the direction of diversification, complexity, precision and multi cavity, and are gradually changing to the direction of large-scale and long-life with high-tech content. The service life of plastic moulds can be increased by reasonably selecting plastic moulds and improving the processing technology and quality of moulds. In order to meet the development requirements of plastic products in the direction of large-scale and precision, attention should be paid to strengthening the use of new plastic molds. At the same time, energy-saving non quenched and tempered pre hardened plastic mold steel will have broad application prospects

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