Chuzhou Essence Mould Manufacturing Co., Ltd.

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Application Research on Surface Strengthening Technology of Mould Working Parts

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  1.1 Carburizing surface chemical heat treatment

  The carburizing process is a more commonly used(over 80%)mold surface strengthening technology,which is mainly for the surface strengthening of plastic mold cavities.After the carburizing treatment,the working parts of the mold can achieve the effect of“outer hard and inner toughness”,that is,the surface of the working part is obtained with hardness,

  The performance of wear resistance,fatigue strength,etc.is improved,while the core still maintains the original plastic toughness and strength,which meets the requirements for the performance of the working parts of the mold.It has fast percolation speed,deep infiltration layer,low cost,and perfect bonding performance between the infiltration layer and the base parts.

  A smooth transition between the bonding layers is achieved.However,the operating temperature is higher(900~950°C),especially the ion carburizing temperature can reach 1100°C,and the corresponding heat treatment is required after carburizing,which leads to the possibility of deformation of the mold,so the high-precision plastic mold does not This technology is recommended.

  The gas carburizing temperature is generally 920~950°C,comprehensive evaluation by Wang Rongbin test:the most reasonable carbon content of the carburized layer surface is w(C)0.85%~0.95%,the gradient of the outer layer of the carbon layer should be even and gentle.Rough martensite,excessive parasitic,reticulated carbide and black troostite are not allowed in the quenched structure.Too high a carbon mass fraction may cause malignant structures such as reticulated carbides in the microstructure of the mold parts,affecting the quality and life of the mold,and stress concentration and cracking may occur during subsequent processing.

  The ion carburizing temperature is generally 900-960°C.Compared with gas carburizing,ion carburizing has the advantages of high efficiency,small deformation,low pollution,and can handle the surface of mold parts of any shape,and is more suitable for the surface of plastic molds and stamping dies.Strengthen the application in processing.

  1.2 flame surface thermal spraying technology

  Thermal spraying technology is an extremely rapid development of surface strengthening technology.It uses a heat source(arc,ion arc,flame,etc.)to heat the spray material to a molten or semi-molten state,atomize it,and spray it at a certain speed.The surface of the pretreated substrate,relying on physical changes and chemical changes,combined with the substrate,the bonding layer can improve the wear resistance,corrosion resistance,heat resistance and other properties of the mold parts,and the operation is simple and the cost is low.In recent years,the application of this technology in mold surface strengthening has been further developed and improved.Guangzhou Nonferrous Metal Research Institute adopts supersonic spraying cemented carbide technology to make Cr12 stainless steel deep drawing.

  The life of the mold is increased by 3 to 10 times.At the same time,the application of this technology has also made great progress in mold repair.For example,Zhang Xianglin of the State Key Laboratory of Material Forming and Mould Technology of Huazhong University of Science and Technology used supersonic flame spraying(HVOF)technology to prepare nanostructures on the surface of Cr12MoV mold steel.WC12Co cermet coating,the average shear strength of the coating was measured to be 150.8 MPa,the bonding strength of the coating was greater than 80 MPa,and the coating hardness was higher than 1000 HV.After the cold extrusion die is repaired by HVOF technology,it can fully meet the requirements of the enterprise.

  1.3 composite surface plating technology

  Electroplating technology is a technique for electrochemically depositing metal or metallization on the surface of a substrate.Electroplating hard chrome and hard nickel are the traditional techniques for surface treatment of plastic molds in China.The technology is carried out at near room temperature,the mold performance is almost unaffected,and there is no serious deformation.

  At the same time,the surface roughness of the plating layer is low and the hardness is increased to 800 HV.However,there are still many problems,such as:low corrosion resistance,grooves and deep holes cannot be treated,which limits its application in mold strengthening.Currently,it can only be used to strengthen the wear resistance of ordinary plastic molds.A plastic mold with a complex shape and high corrosion resistance.

  At present,composite plating is the most dynamic field of coating technology application in the mold industry.Composite brush plating strengthens the mold cavity surface and can also be used to repair mold cavity surfaces.It has been found that an amorphous coating(0.01 to 0.02 mm)can be applied to the surface of the mold cavity to prolong the life by 0.5 to 1.0 times.There are many types of particles that can be added into the composite coating,and the parameter adjustment range is wide,and the operability is strong,which fully reflects the diversity and comprehensiveness of the coating.Yu Tongmin and Liu Guichang of Dalian University of Technology used Ni-P-PTFE composite plating to strengthen the surface of UPVC pipe fittings,which solved the corrosion effect of UPVC materials on the surface of the mold,and achieved the comprehensive performance requirements of wear resistance and corrosion resistance of the mold forming surface.But its hardness is slightly lower.For this reason,Fan Huiyu of Harbin Institute of Technology,based on Ni-P,composited PTFE with SiC particles and applied it to glass fiber reinforced plastic molding dies.Practice has shown that it can increase its life by about 10 times.

  1.4 PVD,CVD,PCVD surface coating technology

  The coating technology,also known as vapor deposition technology,deposits a stable compound with special properties on the surface of the working part of the mold to form a super-hard coating,which makes the working parts of the mold have excellent performance.Stabilizing compounds with higher frequency in the industry mainly include TiC,TiN,SiN and the like.

  Physical vapor deposition(PVD)is a practical technique for physically depositing a coating material on a surface of a substrate after vaporization of the coating material.The technology has been applied since the beginning of the 20th century.It has developed rapidly in the last 30 years and has become a new technology with broad application prospects.It has gradually developed into an environmentally friendly and clean trend,mainly used to manufacture high precision cold working molds..Jiangxi Science

  Peng Wenzhao and Zhang Deyuan of the Institute of Applied Physics of the Institute used the multi-arc ion plating method to carry out the actual service life test of 20 cold extrusion punches treated with TiN coating,and found that their lifespan increased by more than 1.5 times;Lin of Guangzhou Nonferrous Metal Research Institute Song Sheng and Dai Mingjiang conducted a detailed study on the application of physical vapor deposition hard film on tooling,and pointed out that this technology can significantly improve the service life of the mold and the processing quality of the workpiece.However,the PVD method also has disadvantages such as poor coating properties,and there are certain restrictions on the processing of the surface of the mold parts having complicated shapes.

  Chemical vapor deposition(CVD)is a practical technique for chemically reacting a gas on the surface of a substrate material to form a coating layer in the range of 900 to 2000°C.The technology has a high deposition temperature and a firm bond,and there is almost no requirement for the surface shape of the mold parts.For example,parts with complicated shapes or grooves and small holes can be uniformly coated to make up for the defects related to physical vapor deposition,for example,The TiC coating often used in the surface strengthening of the mold has high hardness,good wear resistance,small friction coefficient,good friction reducing property,strong anti-seizure property,and greatly improves the service life of the mold.However,the CVD method has a high processing temperature and still requires quenching treatment,which causes defects such as large deformation,and thus the use of this technique is limited in the manufacture of a high-precision mold.

  Plasma Enhanced Chemical Vapor Deposition(PCVD)is a practical method for enhancing the chemical activity of reactants by glow discharge,promoting chemical reaction between gas phases,and depositing high-quality coatings at low temperatures.It is a treatment method between CVD and PVD..The PCVD method is applied to the surface of the mold working part,and the economic benefits are proved to be considerable.Zhang Yecheng and Zhang Jin of Chongqing Institute of Technology studied the application of PCVD technology in mold strengthening,and found that the deposition of TiC on the W18Cr4V cold extrusion die by PCVD technology is more than 10 times longer than that of the non-deposited film layer;The PCVD method can be used to improve the life of the mold by 1 to 4 times.Professor Tao Ye of Beijing University of Aeronautics and Astronautics has established a research laboratory for PCVD surface intensification technology,designed and manufactured test equipment and auxiliary facilities,and received timely funding from the Natural Science Foundation.The project team developed a mold surface strengthening technology based on PCVD composite infiltration method,which has the advantages of low process temperature,good uniformity and high bonding strength.It is suitable for the preparation of all high temperature tempering molds and some low temperature tempering molds.The only one is suitable for both tool strengthening and shape complexing.

  Hybrid mold surface enhanced vapor deposition surface strengthening technology.It can be seen that the application of PCVD technology in the field of mold part reinforcement has made some achievements.

  And the application prospects are very broad.

  1.5 high energy beam enhancement technology

  High-energy beam enhancement technology has the advantages of non-contact,precise controllability,wide material adaptability,strong flexibility,excellent quality,resource saving and environmental friendliness.It can be used for high-volume and high-efficiency automated production,as well as for multi-variety and small batches.Processing,and even the customization of personalized products,is an indispensable important technology in the mold manufacturing industry.Among them,the ion implantation technology is widely used in the fields of cold working molds,hot working molds and plastic molds with its almost perfect strengthening effect,and its average life expectancy can generally be increased by 2 to 10 times.Has significant application value.

  2.Prospects for application of surface strengthening technology in mold manufacturing

  According to the research,rare earth elements can strengthen the surface,increase the seepage speed,purify the stable grain boundary,and improve the surface structure,physical and chemical properties and mechanical processing properties of the mold 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 to the Ni-Cu-P-MoS2 coating,the wear life of the mold cavity surface can be extended by nearly 5 times.In addition,rare earth elements have obvious improvement effects in chemical deposition,electrodeposition,spray coating and laser coating,but the effect is not very stable.It can be seen that the application of rare earth elements in mold manufacturing will be an important direction for future research.

  With the rapid development of nanotechnology,it is effective in improving the productivity and life of the mold.However,there are still many imperfections in this technology.There are still many tasks to be done,such as:complex mold cavity surface coating unevenness,unclear deposition parameters,and unclear mechanism for surface strengthening of mold parts.

  3.Conclusion

  The surface strengthening technology of mold working parts can make up for some shortcomings of current mold materials to a certain extent,and has shown great development potential.However,there are still some shortcomings in the current surface strengthening technology of mold parts,and its application is also affected.Certain restrictions,as long as focus on research and development,will certainly accelerate and improve the application of surface strengthening technology in the mold manufacturing process.

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