PVD coating technology of the most explosive die

2022-10-15
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Tools and dies PVD coating technology

-- recall the days of Longji

1 Abstract

2 The development of vacuum coating technology

vacuum coating technology has not started for a long time. It was only in the 1960s that CVD (chemical vapor deposition) technology was applied to cemented carbide tools in the world. Because this technology needs to be carried out at high temperature (the process temperature is higher than 1000 C), the coating type is single and has great limitations, so its early development is not satisfactory

by the end of 1970s, PVD (physical vapor deposition) technology began to appear, creating a Xintiandi full of bright prospects for vacuum coating. Later, PVD coating technology has developed rapidly in a short period of two or three decades. The reason is that it forms a film in the vacuum sealed cavity, which is almost free of any environmental pollution problems and conducive to environmental protection; Because it can get a bright and luxurious surface, in terms of color, there are seven mature colors, silver, transparent color, golden yellow, black, and any color from golden yellow to black, which can be described as colorful, and can meet various decorative needs; Due to PVD technology, ceramic coatings and composite coatings with high hardness and wear resistance that are difficult to obtain by other methods can be easily obtained. When applied to tooling and molds, the service life can be doubled, and the effect of low cost and high income can be better realized; In addition, PVD coating technology has two characteristics of low temperature and high energy, and can form films on almost any substrate. Therefore, it is not surprising that it has a wide range of applications and its rapid development. With the development of vacuum coating technology, new technologies such as PCVD (physical chemical vapor deposition) and mt-cvd (medium temperature chemical vapor deposition) have emerged. Various coating equipment and coating processes are emerging in endlessly. Now in this field, a hundred flowers have bloomed and a hundred schools of thought are competing

At the same time, we should also clearly see that the development of vacuum coating technology is seriously unbalanced. Due to the extremely poor working environment of knives and molds, the requirements for film adhesion are much higher than those of decorative coatings. Therefore, although the decorative coating manufacturers have been all over the country, there are not many manufacturers who can produce tooling coating. Coupled with the lack of after-sales service of tool and mold coating, so far, most domestic coating equipment manufacturers cannot provide complete tool coating technology (including pretreatment process, coating process, post-treatment process, detection technology when the sensor is under tension, application technology of coated tools and molds, etc.). In addition, it also requires process technicians to be proficient in coating professional knowledge, It should also have solid knowledge of metal materials and heat treatment, knowledge of surface pretreatment before tooling coating, reasonable selection of cutting tools and tooling coating, and technical requirements for machine use. If there is a problem in any link, it will give users a conclusion that the use effect is not ideal. All these have seriously restricted the application of this technology in cutting tools and molds

on the other hand, because this technology is a new frontier discipline between materials science, physics, electronics, chemistry and other disciplines, and most of the few backbone manufacturers that apply it in the field of tool and mold production in China also follow the path of introducing advanced equipment and process technology from abroad, which still needs a process of digestion and absorption, At present, the domestic technical force in this field is not commensurate with its development, and it is urgent to catch up

3. Basic concept and characteristics of PVD coating

pvd is the abbreviation of "physical vapor deposition", which means physical vapor deposition. Now we generally call vacuum evaporation, sputtering, ion plating, etc. as physical vapor deposition

there are two mature PVD methods: multi arc plating and magnetron sputtering plating. The multi arc plating equipment is simple in structure and easy to operate. Its ion evaporation source can work by the power supply of the electric welding machine, and its arc striking process is also similar to that of electric welding. Specifically, under a certain process pressure, the arc striking needle briefly contacts and disconnects with the evaporation ion source to discharge the gas. The main cause of multi arc plating is the continuous formation of a molten pool on the surface of the evaporation source with the help of constantly moving arc spots, so that the metal is evaporated and deposited on the substrate to obtain a thin film layer. Compared with magnetron sputtering, it not only has the advantages of high target utilization, but also has the advantages of high metal ion ionization rate and strong adhesion between the film and the substrate. In addition, the color of multi arc plating coating is relatively stable, especially when making tin coating, it is easy to get the same stable golden yellow in each batch, which is beyond the reach of magnetron sputtering method. The disadvantage of multi arc plating is that when the coating thickness reaches 0.3 under the condition of low temperature coating with traditional DC power supply μ M, the deposition rate is close to the reflectivity, and the film formation becomes very difficult. Moreover, the film surface began to become hazy. Another disadvantage of multi arc plating is that because the metal evaporates after melting, the deposited particles are large, the density is low, and the wear resistance is worse than that of magnetron sputtering

it can be seen that multi arc coating and magnetron sputtering coating have their own advantages and disadvantages. In order to give full play to their respective advantages and realize complementarity, the coating machine integrating multi arc technology and magnetron technology came into being. In the process, there is a new method of multi arc plating, then using magnetron sputtering to thicken the coating, and finally using multi arc plating to achieve the final stable surface coating color

about in the middle and late 1980s, hot cathode electron gun evaporation ion plating and hot cathode arc magnetron plasma coating machines appeared, with good application effects, making tin coated tools widely used soon. Among them, the hot cathode electron gun evaporates ion plating, uses the copper crucible to heat and melt the plated metal material, uses the tantalum filament to heat and degass the workpiece, and uses the electron gun to enhance the ionization rate, which can not only obtain a thickness of 3-5 μ M, and its adhesion and wear resistance are excellent, and it is difficult to remove it even by grinding. But these devices are only suitable for tin coating or pure metal film. For multi-component coating or composite coating, it is difficult to meet the requirements of high-speed cutting of high hardness materials and the diversity of mold applications

at present, based on the traditional magnetron sputtering principle, some developed countries (such as cemecon in Germany, art-teer in Britain and PLATIT in Switzerland) use unbalanced magnetic field to replace the original balanced magnetic field, 50KHz intermediate frequency power supply to replace the original DC power supply, pulse power supply to replace the previous DC bias voltage, and adopt auxiliary anode technology, which gradually matures magnetron sputtering technology and has been widely used in mold coating, At present, the coatings that have been stably produced mainly include TiAlN, AlTiN, TiB2, DLC and CrN. Such equipment has also been introduced in Guangdong, Jiangsu, Guizhou, Zhuzhou and other places in China, which has a great potential to start a prairie fire

4. Modern coating equipment (uniform heating, the enterprise has expanded three production lines, temperature measurement technology, unbalanced magnetron sputtering technology, auxiliary anode technology, medium frequency power supply, pulse technology) modern coating equipment is mainly composed of vacuum chamber, vacuum acquisition part, vacuum measurement part, power supply part, process gas input system, mechanical transmission part, heating and temperature measuring parts, ion evaporation or sputtering source Water cooling system

4.1 vacuum chamber

coating equipment mainly has two forms: continuous coating production line and single chamber coating machine. Because the mold coating has high requirements for heating and mechanical transmission parts, and the shape and size of the mold are very different, the continuous coating production line is usually difficult to meet the requirements, so the single chamber coating machine must be used

4.2 vacuum obtaining part

in vacuum technology, the vacuum obtaining part is an important part. Due to the requirements of high adhesion of the coating of industrial modules, the background vacuum before the coating process is better than 6Mpa, and the vacuum after the coating process can even reach more than 0.06mpa. Therefore, it is very important to reasonably select the vacuum acquisition equipment to achieve high vacuum

at present, there is no pump that can work from atmospheric pressure to near ultra-high vacuum. Therefore, the acquisition of vacuum cannot be achieved by a vacuum equipment and method. Several pumps must be used together, such as mechanical pump, molecular pump system, etc

4.3 vacuum measurement part

the vacuum measurement part of the vacuum system is to measure the pressure in the vacuum chamber. Like a vacuum pump, it should not be excluded according to its situation. There is a kind of vacuum meter that can measure the whole vacuum range. Therefore, people have made many kinds of vacuum meters according to different principles and requirements

4.4 power supply part

the target power supply mainly includes DC power supply (such as mdx) and intermediate frequency power supply (such as PE, peii and pincal produced by American AE company); The workpiece itself usually needs to add DC power supply (such as mdx), pulse power supply (such as pincal+, produced by AE company in the United States), or radio frequency power supply (RF)

4.5 process gas input system

process gases, such as argon (AR), krypton (KR), nitrogen (N2), acetylene (C2H2), methane (CH4), hydrogen (H2), oxygen (O2), etc., are generally supplied by gas cylinders, through gas pressure reducing valves, gas stop valves, pipelines, gas flow meters, solenoid valves, piezoelectric valves, and then into the vacuum chamber. The advantages of this gas input system are that the pipeline is simple and bright, and it is easy to repair or replace gas cylinders. The coating machines do not affect each other. There are also cases where multiple coating machines share a group of gas cylinders, which may be seen in some large-scale coating workshops. Its advantage is to reduce the consumption of gas cylinders, and unify the planning and layout. The disadvantage is that the chance of air leakage increases due to the increase of joints. Moreover, the coating machines will interfere with each other, and the pipeline leakage of one coating machine may affect the product quality of other coating machines. In addition, when replacing gas cylinders, it must be ensured that all hosts are in a non gas state

4.6 the coating of the cutting tools in the mechanical transmission part requires that the thickness of the periphery must be uniform, so there must be three rotations in the coating process to meet the requirements. That is, when the large workpiece table is required to rotate (I), the small workpiece bearing table also rotates (II), and the workpiece itself can rotate at the same time (III)

in mechanical design, generally, there is a large driving gear in the center of the bottom of the large workpiece turntable, surrounded by some small star wheels to mesh with it, and then use the shift fork to move the workpiece to rotate. Of course, when making mold coating, generally two rotations are enough, but the bearing capacity of the gear must be greatly enhanced

4.7 heating and temperature measurement part

when making the mold coating, how to ensure that the plated workpiece is evenly heated is much more important than the heating of the decorative coating. Generally, the tooling coating equipment has two front and rear heaters, and the temperature is measured and controlled by thermocouples. However, due to the different clamping positions of thermocouples, the temperature reading cannot be the real temperature of the workpiece. There are many ways to measure the real temperature of the workpiece. Here is a simple and easy surface thermometer method. The working principle of the thermometer is that when the thermometer is heated, the spring at the bottom will be heated and expanded, so that the pointer pushes the positioning pointer to rotate until the maximum temperature. When cooling down, the spring shrinks and the pointer rotates in the opposite direction, but the positioning pointer remains at the highest temperature position. After opening the door, read the temperature indicated by the positioning pointer, that is, the vacuum chamber

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