Application summary and exhibition of surface engi

2022-07-23
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Summary and Prospect of surface engineering technology in mold manufacturing Abstract: several kinds of surface engineering technologies widely used in mold manufacturing are briefly summarized, and their performance indexes and economy are compared. The application progress of rare earth surface engineering technology in mold manufacturing was introduced. The application of nano surface engineering technology in mold manufacturing is prospected

key words: mold manufacturing; Surface engineering technology; Rare earth surface engineering; Nano surface engineering

introduction

experts from the International Mold Association believe that mold is the emperor of metal processing industry. And mold material is the foundation of mold industry. However, even the new mold materials are still difficult to meet the requirements of high comprehensive performance of the mold. Surface engineering is an active and rapidly developing branch in the field of material science and engineering. Surface engineering

has the comprehensiveness of disciplines, the diversity of means, the wide range of functions, the potential innovation, the environmental protection, the strong practicality and the huge efficiency, so it is valued by all walks of life. The application of surface engineering technology in mold manufacturing makes up for the shortage of mold materials to a great extent

there are a wide range of surface engineering technologies that can be used in mold manufacturing, including traditional surface quenching technology, thermal diffusion technology, surfacing technology and hard chromium plating technology, as well as laser surface strengthening technology, physical vapor deposition technology (PVD), chemical vapor deposition technology (CVC), ion implantation technology, thermal spraying technology, thermal spray welding technology, composite electroplating technology, and Composite brush plating technology and electroless plating technology. The progress of rare earth surface engineering technology and the rise of nano surface engineering technology will further promote the development of surface engineering technology in mold manufacturing. The application of surface engineering technology to the surface treatment of mold cavity can achieve the following purposes:

(1) improve the surface hardness, wear resistance, corrosion resistance and high temperature oxidation resistance of mold cavity, and greatly improve the service life of mold. Improve the anti scratch ability and demoulding ability of the mold cavity surface, so as to improve the productivity

(2) the comprehensive properties of carbon tool steel or low alloy steel after surface coating or alloying treatment can reach or even exceed the performance indexes of high alloy metallized die materials and cemented carbides, which can greatly reduce the material cost

(3) it can simplify the mold manufacturing process and heat treatment process, and reduce the production cost

(4) it can be used to decorate the surface of mold cavity to improve the grade and added value of products

(5) it can be used for mold repair and other remanufacture engineering

1 thermal diffusion technology

thermal diffusion technology is a process in which metallic or non-metallic elements to be infiltrated penetrate the surface of metal materials or workpieces by means of heating diffusion, so as to form a surface alloy layer. Its outstanding feature is that the diffusion layer and the substrate are combined by forming an alloy, which has a high bonding strength, which is unmatched by other coating methods such as electroplating, spraying, electroless plating, and even physical vapor deposition. Alloy elements commonly used for thermal diffusion include carbon, nitrogen, silicon, boron, aluminum, vanadium, titanium, tungsten, niobium, sulfur, etc. The above elements have been applied to the surface strengthening of various mold cavities to varying degrees. With the continuous development of thermal diffusion technology, binary and even multivariate CO diffusion technology plays an increasingly important role in die surface strengthening. For different infiltration elements or different types of dies, the best infiltration processes are also different. Here, several thermal diffusion processes which are most used in die surface strengthening are introduced

1.1 carburizing

carburizing has the characteristics of fast carburizing speed, deep carburizing layer, easy control of hardness gradient and composition gradient of carburizing layer, and low cost. It can effectively improve the surface hardness, wear resistance and fatigue strength of materials at room temperature. The first aspect of carburizing process applied to die surface strengthening is the carburization of low and medium carbon steel. Carburizing applied to cold working, hot working and plastic moulds can improve the service life of moulds. For injection molds, especially when forming plastic products with abrasive wear on the cavity, 20\e steel can be used to roughen the mold, carburize the cavity surface, and then put into use after finishing and polishing. In addition to reducing the surface roughness, the wear resistance of the mold will be correspondingly improved. Another example is the 3gr2w8v steel die-casting mold, which is carburized first, then quenched at 1140 ℃ -1150 ℃, and tempered twice at 550 ℃. The surface hardness can reach HRC, which increases the service life of the die-casting non-ferrous metals and their alloys by 1.8 - 3.0 times

the second aspect of carburizing process applied to die surface strengthening is "carbide dispersion precipitation carburizing", referred to as CD carburizing method for short. It uses die steel containing a large number of strong carbide forming elements (such as Cr, Ti, Mo, V) to heat in the carburizing atmosphere. While the carbon atoms diffuse from the surface to the inside, a large number of

loose alloy carbides, such as (CR · FE) 7C3, (Fe · CR) 3C, v4c3, tic, will precipitate in the carburizing layer, thus realizing CD carburization. In the CD carburized layer, the surface carbon content (mass fraction, the same below) of the carburized layer is as high as 2% - 3%, the content of dispersed carbide is more than 50%, and the carbide is fine and evenly distributed. High hardness and excellent wear resistance can be obtained by direct quenching or re quenching and tempering of CD carburized parts. There are no coarse eutectic carbides and severe carbide segregation in the center of the die carburized by CD, such as Cr12 die steel and high speed steel, so the center toughness is times higher than that of Cr12MoV steel. The practice shows that the service life of CD carburizing die greatly exceeds that of Cr12 cold working die steel and high speed steel, which account for the first place in cold working die steel consumption

when carburizing various molds, the main carburizing process methods include solid powder carburizing, gas carburizing and vacuum carburizing and ion carburizing, which have developed rapidly in the past 20 years. Among them, solid carburizing and gas carburizing are widely used, but vacuum carburizing and ion carburizing technology will play a more and more important role in the surface treatment of dies, especially precision dies, because they have the characteristics of fast carburizing speed, uniform carburizing layer, gentle carbon concentration gradient and workpiece deformation

1.2 gas method low temperature thermal diffusion

gas method low temperature surface thermal diffusion process plays a very important role in the surface strengthening treatment of dies. The treatment process is simple and the diffusion temperature is low. It can meet the requirements of cold working mold, development cooperation mode, hot working mold of specific products and plastic mold. The commonly used diffusion processes include nitriding, soft nitriding (ferritic nitrocarburizing), oxygen nitrocarburizing, sulfur nitrocarburizing, and even sulfur carbon nitrogen, oxygen nitrogen sulfur ternary nitrocarburizing

1.2.1 gas nitriding and ion nitriding process

the process of penetrating nitrogen into steel parts is called nitriding or nitriding of steel. The hardness of nitrided layer is high (HV), and its wear resistance, fatigue strength, red hardness and anti bite are better than those of carburized layer. Due to the low nitriding temperature (generally 480 ℃ -600 ℃), the workpiece deformation is very small, especially suitable for the surface strengthening of some precision molds. For example, after tempering and nitriding at 520 ℃ -540 ℃, the service life of 3Cr2W8V steel die casting and extrusion dies is times longer than that of non nitriding dies. For another example, the hot stamping die imported from Germany was dissected and analyzed, and it was found that its surface was about 140 μ M. Many die-casting molds made of H13 steel in the United States are subject to nitriding treatment, and nitriding is used instead of one-time tempering. The surface hardness is as high as HRC, while the core hardness of the mold is low and the toughness is good, so as to obtain excellent comprehensive mechanical performance for accelerating the development of the copper based new material industry

gas nitriding is the most widely used nitriding process. Ion nitriding is a process developed to solve the problems of low work efficiency and long time of gas nitriding process. Its characteristics are fast nitriding speed, easy control of nitriding layer composition and gradient, energy saving, gas saving, good quality of nitriding layer, good working environment, etc

1.2.2 gas soft nitriding (ferritic nitrocarburizing)

soft nitriding is a thermal diffusion process in which the steel parts are heated at about 570 ℃ and the urea, ammonia or alcohol cracking gas is used as the penetrating agent to simultaneously expand the carbon and nitrogen atoms into the steel. Gas soft nitriding is faster than gas nitriding and requires less cost. Its application in cold and hot working die steel can improve the wear resistance, high temperature oxidation resistance and adhesion resistance of the die

2 thermal spraying and spray welding technology

2.1 thermal spraying technology

thermal spraying technology is a surface coating method that heats the sprayed materials to the molten or semi molten state, atomizes and accelerates them with high-speed air flow, so that they can be sprayed to the workpiece surface at high speed to form a coating with special properties such as wear resistance, corrosion resistance and high-temperature oxidation resistance. According to the types of heat sources for heating spraying materials, there are mainly three types: gas method, electrical method and high-energy beam heating method. Because the thermal spray coating is not dense and has low bonding strength with the substrate, it is difficult to play a role in the surface strengthening of the die. Therefore, the thermal spray welding process that the coating remelting makes it form metallurgical bonding with the substrate and reduces the porosity came into being

2.2 thermal spray welding technology

the thermal spray welding process, especially the oxyacetylene flame spray welding process, is simple, has less equipment investment and is easy to promote. It is widely used to strengthen the mold surface, improve the corrosion resistance, wear resistance and prolong the service life. The economic benefits are very considerable

3 vapor deposition technology

according to the film-forming mechanism, vapor deposition technology can be divided into chemical vapor deposition (CVD) and physical vapor deposition (PVD)

3.1 physical vapor deposition

under vacuum conditions, atoms or molecules produced by various physical methods are deposited on the substrate to form a film or coating, which is called physical vapor deposition. According to the difference of physical mechanism during deposition, it can be divided into three types: vacuum evaporation (VE), vacuum sputtering (VS) and ion plating (IP). Among them, tin and tic wear-resistant coatings plated by multi arc ion plating have been widely used in tool and die surface strengthening

3.2 chemical vapor deposition

chemical vapor deposition is a surface technology that uses volatile compounds or elemental vapors containing various elements in the film layer to produce a vapor phase chemical reaction on the surface of the hot substrate, and the reaction products form a deposited coating. This technology has played a great role in the mechanical industry, especially the deposition of some super hard films such as nitrides, carbides, diamonds and DLC, which greatly improves the wear resistance and corrosion resistance of workpieces such as molds

4 composite electroplating technology

the application of electroplated coatings is mainly in corrosion prevention and decoration. The appearance of composite electrodeposited coating provides a promising method for solving high temperature corrosion, high temperature strength and wear. Various wear-resistant coatings can be prepared by composite electroplating. For example, the composite coating of matrix metal diamond particles and Ni-P-SiC composite coating have good wear resistance on the surface of tools and dies. In recent years, in order to improve the wear resistance of composite coatings, the following measures have been taken:

(1) alloy coatings, including Ni Co, Ni Mn, Ni Fe and Ni-P coatings, are used to replace single metal coatings to greatly improve the hardness of the die surface

(2) the wear resistance of hard Cr layer can be increased by 1-3 times than that of pure Cr layer

(3) Ni pjfe composite coating prepared by using polytetrafluoroethylene (pjfe) as co deposited particles is commonly used for demoulding coating of rubber mold and injection mold. The test results on the friction and wear tester show that the wear loss of Ni pjfe composite coating is about 1/10 of that of hard Cr coating and about 1/50 of that of bright Ni coating

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