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Study on the application of surface reinforcement of die working parts


For surface strengthening technology in the application of the working parts of the mold manufacturing process were studied, analyzed the technology of functional, environmental protection and the advantages of the synergistic in the mold manufacturing costs, quality of mould and die life. The results show that the optimal matching point of the selection factors can make up the deficiency of the current mould materials to a certain extent, which can significantly improve the die life and quality.

Surface strengthening technology in mould manufacturing is to point to the surface after preprocessing the mould work part, through a single or composite surface processing technology, make the mould work part to obtain the required surface or comprehensive performance of professional reinforcement technology. The functional, environmental and synergistic advantages of the technology play an important role in mold manufacturing cost, mold quality and die life. In production, considering the characteristics of the technology, working conditions of the mold and production of economic factors, such as, selecting the best match of the factors, can significantly improve die life, quality, access to the prominent economic benefits.
1. The application status of surface strengthening technology in mold manufacturing.
1.1 chemical heat treatment on carburizing surface.
The carburizing process is a more commonly used (80%) of the surface strengthening technology of the mould, which is mainly aimed at the surface strengthening of the plastic mold cavity. The working parts of the mould after carburizing can achieve the effect of "external hard inner toughness", i.e. the surface of the working part gets the hardness,.
The wear resistance, fatigue strength and other properties are improved, while the core remains the original plastic toughness and strength, which meets the requirements for the performance of the mold working parts. With fast seepage, deep penetration, low cost, and perfect bonding performance between the infiltration layer and the matrix parts,
A smooth transition between the bonding layers. But higher operating temperature (900 ~ 950 ℃), especially ion carburizing temperature can reach 1100 ℃, and after carburizing and corresponding heat treatment, leading to the possibility of mold deformation increase, so the high precision plastic mold the technology is not recommended.
Gas carburizing temperature is 920 ~ 950 ℃, commonly through Wang Rongbin test comprehensive evaluation: the most reasonable carburizing layer surface carbon content for w (C) 0.85% ~ 0.95%, permeability layer outside-in carbon mass fraction gradient should be uniform flat, quenching in the organization is not allowed to have a thick strips martensite, too much the paralympic, troostite carbide network and black. The high carbon mass fraction were molded parts organization carbide network in malignant tissue, such as, affecting the service life of die quality and liable to occur in the subsequent process of stress concentration, the phenomenon such as cracks.
Ion carburizing temperature is 900 ~ 960 ℃, compared with gas carburizing, ion carburizing with high efficiency, small deformation, pollution and can handle any shape of surface mould parts, etc, is more suitable for the plastic mould and stamping die surface strengthening processing of the application.
1.2 flame surface thermal spraying technology.
Thermal spraying technology is a new surface strengthening technology development is very rapid, it is the use of heat sources (electric arc, arc ion, flame, etc.) will be heated to melt coating material or partially molten state, and make it spray, spray at a certain speed to after pretreatment of substrate surface, relying on the physical and chemical changes, combined with the matrix of process method, the binding layer, can improve the wear resistance of mold parts, corrosion resistant, heat resistant, such as performance, and easy operation, low cost. In recent years, the application of this technique has been further developed and improved in the application of the surface reinforcement of the die, and the technology of the ultrasonic spraying hard alloy is adopted by guangzhou nonferrous metal research institute to make the Cr12 stainless steel drawing deep.
The die life has been increased by 3 ~ 10 times. At the same time, the technology also made great progress in the mold repair, such as huazhong university of science and technology, material forming and mould technology state key laboratory of Zhang Xianglin using supersonic flame spraying (HVOF) technology, such as in Cr12MoV die steel surface preparation of the nanometer structure WC12Co metal ceramic coating, coating can be measured the average shear strength of 150.8 MPa, the coating bond strength of more than 80 MPa, the coating hardness is higher than 1000 hv. The application of HVOF technology to the cold extrusion mould can meet the requirements of the enterprise.
1.3 composite surface plating technology.
Electroplating technology is an electrochemical method for deposition of metal or metallization on the substrate surface. Electroplating hard chromium and hard nickel is the traditional technology of surface treatment of plastic mould in China. The technology is carried out at near room temperature, the mould performance is almost impervious, and there is no serious deformation.
Meanwhile, the surface roughness of electroplating layer is low, and the hardness is increased to 800HV. But there are still many problems, such as corrosion resistance is not high, groove, deep hole can't handle, make its application in the mold reinforced by certain restrictions, only can be used to strengthen the common plastic mould wearability, shall not be applicable to complicated shape and high corrosion resistance requirements of plastic mold.
At present, composite plating is the most dynamic application of coating technology in the mould industry. Composite brush plating can strengthen the surface of die cavity and repair mold cavity surface. The study found that the non-crystalline coating (0.01 ~ 0.02 mm) on the surface of the mold cavity can extend the life span 0.5 ~ 1.0 times. In the composite coating, the variety of particles can be added, and the range of parameter adjustment is wide and operable, which fully reflects the diversity and comprehensiveness of the coating. Of dalian university of technology in such as sensitive, gui-chang liu Ni - P - PTFE composite plating for UPVC pipe fittings mold surface strengthening, solve the UPVC material corrosion on the surface of the mould has obvious effect, achieve molding surface wear-resisting corrosion resistance comprehensive performance requirements, but the hardness is a bit low. Harbin institute of technology for this fan will jade on the basis of Ni - P, PTFE and SiC particles in the composite application in glass fiber reinforced plastic molding mold, practice shows can make its life by about 10 times.

1.4 surface coating technology of PVD, CVD and PCVD
Coating technology is vapor deposition technology, is to have special performance of stable compounds deposited on the working parts of the mold surface, formation of hard coating, make the mould work part has excellent performance. The stable compounds with high frequency of use in industry mainly include TiC, TiN, sine and so on.
Physical gas phase deposition (PVD) is a practical technique for the deposition of coating materials on the substrate surface by means of physical methods. The technology application in the beginning of the 20th century, is developing rapidly in the recent 30 years, as a door has a broad application prospect of new technology, and gradually to the development trend of environmental protection, clean type, mainly used in the manufacture of high precision cold work mould. Jiangxi science.
School of institute of applied physics Peng Wenyi, de-yuan zhang multi arc ion plating method of 20 after TiN coating processing trials on actual service life of cold extrusion punches, found that the life expectancy increased by 1.5 times above; Guangzhou institute of nonferrous metals song-sheng Lin, generation of Ming jiang for physical vapor deposition of hard film on advanced application has carried on the detailed research, pointed out that the technology can significantly improve the quality of the service life of die and workpiece machining. However, the PVD method also has the disadvantages such as the plating error, and there are some restrictions on the surface treatment of the complex mould parts.
Chemical vapor deposition (CVD) is within the range of 900 ~ 2000 ℃ using chemical methods to make gas in the surface of substrate material in chemical reactions and form a layer of practical technology. The technology deposition combined with strong, high temperature, coating surface shape of molded parts almost no requirements, such as complex shape parts or with grooves and holes are evenly coated, make up the physical vapor deposition related defects, such as the frequently used in the mold surface strengthening of TiC coating high hardness, good wear resistance, low friction factor, anti-friction and bite resistance is strong, increase the service life of mould. However, the treatment of high temperature in CVD method still needs to be treated with quenching, which can lead to the defects such as large deformation and so on. Therefore, the use of this technology in the manufacture of high-precision die is limited.
Plasma enhanced chemical vapor deposition (PCVD) is the use of glow discharge to enhance the chemical activity of reactants, promote the gas phase chemical reactions, with high quality at low temperature deposition coating of practical technology, is a kind of processing between CVD and PVD method. The coating of coating on the surface of die working parts is coated with PCVD method, and the economic benefit is very considerable. Chongqing institute of technology of the lobe, Zhang Jin PCVD technology application in the mold to strengthen research, found that using PCVD technology in W18Cr4V deposits a layer of TiC in cold extrusion die, die life than no deposited film layer increased by more than 10 times; The PCVD method can be used to improve the die life of plastic products by 1 ~ 4 times. Beijing university of aeronautics and astronautics professor mold set up PCVD surface strengthening technology research laboratory, the experimental equipment was designed independently and ancillary facilities, and sponsored by the natural science foundation of China in time. Program is developed based on composite plating PCVD method of mould surface strengthening technology, a low temperature, are good plating processes and high bonding strength, applicable to all the preparation of high temperature tempering mould and parts of low temperature tempering mould, is currently the only applicable to cutting tool as well as a way of strengthening and is suitable for the complex shape.
The surface reinforcement of the surface of the mixed mould is enhanced. Therefore, the application of PCVD technology in the field of mold parts strengthening has been achieved.
And the application prospect is very broad.
1.5 high energy beam strengthening technology.
High energy beam reinforcement technology with non contact material, control precision, wide adaptability, strong flexibility, quality, resource saving and environment friendly and other comprehensive advantages, can be used for both mass efficient automation production, and is applicable to many varieties, small batch processing, custom-made personalized products, even is an important and indispensable technologies in mould manufacturing. Among them, the ion implantation technology in its almost perfect strengthening effect in cold work mould, hot-work die and plastic mould is widely used in areas such as, its life expectancy can improve the general 2 ~ 10 times. Significant application value.

2. The application prospect of surface strengthening technology in die making.

According to the research, rare earth elements can strengthen the surface, improve the seepage speed, purify the stable grain boundary, and improve the surface organization, physical and chemical properties and mechanical processing properties of the mould parts. The application of rare earth elements in the process of composite surface strengthening technology can obtain more obvious effects. If rare earth is added in the Ni-Cu- p-mos2 coating, the wear-resisting life of the mold cavity can be increased by nearly five times. In addition, rare earth elements in the chemical deposition, electroplating, spraying and laser coating has obvious improvement in such aspects as function, but the effect is not very stable, visible elements used in mould manufacturing will be the important direction of future research.
With the rapid development of nanotechnology, it has a remarkable effect in improving the productivity and longevity of the mould. But the technology also has many drawbacks, there are a lot of work to do, such as: uneven complex mold cavity surface coating, the deposition parameters are not clear, for mold parts surface strengthening mechanism is unknown.


3, conclusion


The working parts of the die surface strengthening technology can to a certain extent, make up some shortages die materials at present, and has set up a showing strong development potential, but in terms of the present mould parts surface strengthening technology, there are still some shortage, its application has also been a certain limit, as long as pay attention to the research and development, will accelerate and perfect the application of surface strengthening technology in mould manufacturing process.

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