Vacuum coating technology did not take long to start. It was only in the 1960s that CVD (chemical vapor deposition) technology was applied to cemented carbide tools. Because the technology needs to be carried out at high temperature (process temperature is higher than 1000oC), the coating type is single and the limitation is very large. Therefore, the initial stage of its development is not unsatisfactory.

By the end of the 1970s, PVD (Physical Vapor Deposition) technology began to appear, creating a new world of brilliant prospects for vacuum coatings. After that, PVD coating technology developed rapidly in just two or three decades. The reason is that it forms a film in a vacuum-sealed cavity, and it has almost no environmental pollution problems, which is beneficial to environmental protection; because it can obtain a bright, luxurious surface, in the color, the mature color is seven-color, silver, transparent , Golden yellow, black, and any color from golden yellow to black, can be described as colorful, can meet various decorative needs; and because of PVD technology, you can easily get high hardness and high resistance that are difficult to obtain by other methods Abrasive ceramic coatings and composite coatings are applied to tooling and molds, which can double the life and achieve a low-cost and high-yield effect; in addition, the PVD coating technology has both low temperature and high energy The characteristics can be formed on almost any substrate, so the scope of application is very wide, and its rapid development is not surprising. 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 various coating processes have emerged in an endless stream. Now in this field , Has shown a gratifying scene of a hundred flowers blooming and a hundred schools of thought contending. At the same time, we should also be soberly aware that the development of vacuum coating technology is seriously unbalanced. Due to the extremely harsh working environment of cutters and molds, the requirements for film adhesion are much higher than decorative coatings. Therefore, although there are many manufacturers of decorative coatings all over the world, not many manufacturers can produce tool coatings. Coupled with the lack of after-sales service for cutting tools and molds, so far, most domestic coating equipment manufacturers cannot provide complete tool coating process technology (including pre-treatment process, coating process, post-coating treatment process, inspection Technology, coating tool and mold application technology, etc.), and it also requires process technicians, in addition to proficiency in coating expertise, solid metal materials and heat treatment knowledge, pre-treatment surface coating Knowledge, reasonable choice of tool, mold coating, and technical requirements for use on the machine, etc., if any problem occurs, it will give users the conclusion that the use effect is not ideal. All of these severely restrict the application of this technology to tools and molds. On the other hand, because the technology is an emerging edge discipline between the disciplines of materials science, physics, electronics, chemistry, etc., and it is applied to a few key manufacturers in the field of tool and mold production in China, Most of them are also taking a path of importing advanced equipment and technology from abroad, which still requires a process of digestion and absorption. Therefore, the current domestic technical strength in this field is very disproportionate to its development, and it is urgent to catch up.

Tool coating development status

PVD is the abbreviated form of "Physical Vapor Deposition" in English, which means physical vapor deposition. We now generally refer to vacuum vapor deposition, sputter coating, ion plating, etc. as physical vapor deposition. The more mature PVD methods mainly include multi-arc plating and magnetron sputtering plating. The multi-arc plating equipment has a simple structure and is easy to operate. Its ion evaporation source can be operated by the power supply of the electric welding machine, and its arc starting process is similar to that of electric welding. Specifically, under a certain process pressure, the arc starting needle briefly contacts the evaporating ion source and disconnects to discharge the gas . The reason for the multi-arc plating is mainly to continuously form a molten pool on the surface of the evaporation source by means of the continuously moving arc spot, 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 high utilization rate of the target material, but also has the advantages of high metal ionization rate and strong binding force between the film and the substrate. In addition, the color of the multi-arc coating is relatively stable, especially when making TiN coating, each batch is easy to get the same stable golden yellow, making the magnetron sputtering method unmatched. The disadvantage of multi-arc plating is that under the condition of using traditional DC power supply for low temperature coating, when the coating thickness reaches 0.3μm, the deposition rate is close to the reflectivity, and film formation becomes very difficult. Moreover, the surface of the film starts to become hazy. Another disadvantage of multi-arc plating is that because the metal evaporates after melting, the deposited particles are larger, the density is low, and the wear resistance is worse than that of the magnetron sputtering method. It can be seen that the multi-arc coating and the magnetron sputtering method have their own advantages and disadvantages. In order to maximize their respective advantages and achieve complementarity, a coating machine that combines multi-arc technology and magnetron technology into one comes into being. . In the process, there is a multi-arc plating primer, then the magnetron sputtering method is used to thicken the coating, and finally a new method using multi-arc plating to achieve the final stable surface coating color. In the mid-to-late 1980s, hot cathode electron gun evaporative ion plating, hot cathode arc magnetron plasma coating machines appeared, and the application effect was very good, so that TiN coated cutters were quickly popularized. Among them, the hot cathode electron gun evaporates ion plating, uses the copper crucible to heat and melt the metal material to be coated, uses the tantalum filament to heat and degas the workpiece, and uses the electron gun to enhance the ionization rate. Both the strength and the wear resistance are good, and it is difficult to remove even by grinding. But these devices are only suitable for TiN coating, or pure metal film. For multi-layer coatings or composite coatings, it is difficult to adapt to the requirements of high-speed cutting of high-hardness materials and the diversity of mold applications. At present, some developed countries (such as CemeCon in Germany and ART-TEER in the UK) replace the original balanced magnetic field with a non-equilibrium magnetic field, replace the original DC power supply with 50KHz intermediate frequency power supply, and replace the previous pulse power supply DC bias voltage, using auxiliary anode technology, etc., has gradually matured the magnetron sputtering technology, has been applied in a large number of mold coatings, and now the stable production of coatings are mainly TiAlN, AlTiN, TiB2, DLC, CrN, etc. In China, Guangdong, Jiangsu, Guizhou, Zhuzhou and other places have also introduced such equipment one after another.

Basic components of tool coating equipment

Modern coating equipment (uniform heating technology, temperature measurement technology, unbalanced magnetron sputtering technology, auxiliary anode technology, intermediate frequency power supply, pulse technology) Modern coating equipment is mainly composed of vacuum chamber, vacuum acquisition part, vacuum measurement part, power supply It consists of part, process gas input system, mechanical transmission part, heating and temperature measuring parts, ion evaporation or sputtering source, water cooling system and so on.

1 Vacuum chamber

Coating equipment mainly has two forms: continuous coating production line and single-chamber coating machine. Due to the high requirements for heating and mechanical transmission parts of the mold coating, and the shape and size of the mold are very different, the continuous coating production line is usually difficult to meet A single-chamber coating machine is required.

2 Vacuum acquisition section

In vacuum technology, the vacuum acquisition part is an important part. Due to the high adhesion requirements of the coating of tooling parts, the coating process requires a good background vacuum. It is very important to choose the vacuum to obtain the equipment reasonably and achieve high vacuum. For now, there is no pump that can work from atmospheric pressure to near ultra-high vacuum. Therefore, the vacuum is not achieved by a vacuum equipment and method, and several pumps must be used in combination, such as a mechanical pump and a molecular pump system.

3 Vacuum measurement section

The vacuum measurement part of the vacuum system is to measure the pressure in the vacuum chamber. Like a vacuum pump, no vacuum gauge can measure the entire vacuum range, so people have made many types of vacuum gauges based on different principles and requirements.

4 Power supply section

The target power supply mainly includes DC power supply (such as MDX), intermediate frequency power supply (such as PE, PEII, PINACAL of American AE company); the workpiece itself usually needs to add DC power supply (such as MDX), pulse power (such as PINACAL+ produced by American AE company) Or radio frequency power supply (RF).

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. Gas pressure reducing valve, gas shut-off valve, pipeline, gas flow meter, solenoid valve, piezoelectric valve, and then into the vacuum chamber. The advantage of this gas input system is that the pipeline is simple and clear, and it is easy to repair or replace the gas cylinder. The coating machines do not affect each other. There are also cases where multiple coating machines share a set of gas cylinders, which may be seen in some larger coating workshops. The advantage of it is that it reduces the occupancy of gas cylinders, unified planning and unified layout. The disadvantage is that due to the increased number of joints, the chance of air leakage increases. Moreover, each coating machine will interfere with each other. The air leakage of one coating machine's pipeline may affect the quality of other coating machines. In addition, when replacing gas cylinders, it must be ensured that all hosts are in a non-gassing state.

6 Mechanical transmission part

The coating of the tool 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, while the large workpiece table is required to rotate (I), the small workpiece carrying table also rotates (II), and the workpiece itself can also rotate at the same time (III). In mechanical design, a large driving gear is generally located in the center of the bottom of the large workpiece turntable, surrounded by small star wheels to mesh with it, and then the fork is used to rotate the workpiece to rotate. Of course, when doing mold coating, generally two rotations are enough, but the load capacity of the gear must be greatly enhanced.

7 Heating and temperature measuring part

When making a die coating, it is much more important to ensure that the plated workpiece is heated evenly than the decorative coating. Tool coating equipment generally has two heaters in front and behind, and thermocouples are used to measure and control the temperature. However, because the thermocouples are set differently, the temperature reading cannot be the true temperature of the workpiece. There are many methods to measure the true temperature of the workpiece. Here is a simple and convenient surface temperature method (Surface Thermomeer). The working principle of the thermometer is that when the thermometer is heated, the spring at the bottom will be heated to expand, so that the pointer pushes the positioning pointer to rotate until it reaches the highest temperature. When the temperature drops, the spring contracts and the pointer rotates in the reverse direction, but the positioning pointer remains at the highest temperature position. After opening the door, read the temperature indicated by the positioning pointer, which is the highest position that the surface thermometer has placed when heating in the vacuum chamber Temperature value.

8 ion evaporation and sputtering source

The evaporation source of multi-arc plating is generally a pie shape, commonly known as a pie target. In recent years, rectangular multi-arc targets have also appeared, but no obvious effect has been seen. The round cake target is mounted on the copper target base (cathode base), and the two are screwed. A magnet is installed in the target base. By moving the magnet forward and backward to change the strength of the magnetic field, the moving speed and trajectory of the arc spot can be adjusted. In order to reduce the temperature of the target and the target base, the target base must be continuously fed with cooling water. In order to ensure high electrical and thermal conductivity between the target and the target base, tin (Sn) spacers can also be added between the target and the target base. Magnetron sputtering coating generally uses rectangular or cylindrical targets,

9 Water cooling system

In order to improve the ionization rate of metal atoms during tool coating, each cathode target uses a large power output as much as possible and needs to be fully cooled; moreover, many coatings in tool coatings are heated at 400~500oC, therefore, it is also important to cool the vacuum chamber wall and the various sealing surfaces, so the cooling water is best to use a cold water machine of about 18~20oC for water supply. In order to prevent the low temperature vacuum chamber wall, cathode target and hot air from contacting the water droplets after opening the door, the water cooling system should be able to switch to the hot water supply state about 10 minutes before the door is opened.

Development trend of tool coating technology

1. The coating composition will tend to be diversified and complex

The first generation of PVD coating is mainly based on TiN, and on this basis, a variety of single metal coatings such as TiC, TiCN, ZrN, CrN, and WC have been developed. With the further development of PVD deposition technology, in the aluminum element technology plus coatings, aluminum-containing multi-metal alloy coatings such as TiAIN, TiAICN, etc. have come out one after another. Its wear resistance and red hardness are much improved than single metal coatings. For higher cutting speeds, such as roll cutting, it can reach 150m/min. Later, people considered depositing a variety of different types of coatings on the tool in order to take advantage of different coatings, such as TiN+TiCN+TiN, TiN+TiALN, TiAIN+WC/C, etc. In recent years, PVD coating technology has taken another step forward. Many foreign coating companies have developed and applied pulse coating technology, such as P3E (Pulse Enhanced Electron Emission) technology from Swiss Balzers company. HIP_ (High Ion Pulse, High Energy Particle Pulse) technology from Cemecon, Germany. Both of these new technologies use pulsed electrons to activate the arc evaporation target. Since the process can be operated in an oxygen atmosphere, in theory, almost any metal oxide (such as A12O3, ZrO2, Cr2O3) can be deposited with this process , Ta2O5, etc.) and their compound coatings. At present, Al2O3 coating has entered the practical test stage, and it is believed that it will be widely used in the near future.

2. The application development of coating is more targeted

In order to meet different application requirements, the development and design of coatings are increasingly targeted. In view of the characteristics and requirements of different application fields such as drilling, milling, dry rolling, stamping, drawing, etc., we have developed coatings with comparative advantages in this regard. After continuous efforts and attempts, it has achieved success in certain fields, such as high aluminum content about TiX (Al: Ti 2:1) coating applied to milling, Ti-free coating AICrN application of high-speed dry rolling In the above, the composite coating CrN+TISIN is used in drilling, and the composite coating TIN+TCX is applied in deep-drawing dies, and the service life is significantly better than other coatings. In addition, such as various targeted coatings for corrosion resistance (Crx coating), "self-lubrication (WC/C coating), soft material processing (MoS2 coating), high-hard material processing (CBN, Dimond coating) Layers have already been widely used. Although these coatings have been very successful in their respective fields, with the continuous development of PVD coating technology, new and more targeted coatings will continue to be developed to replace these existing There is a coating.

3. The deposited particles of the coating tend to be nano

With the development of nanotechnology and the advancement of coating technology, nanotool coating has also attracted the attention of researchers and PVD coating service companies. The nanometerization of the deposited particles of the coating can enhance the bonding strength between the coating and the substrate and each layer, and at the same time can reduce the surface roughness of the coating. At present, the deposited particles of most coatings are still relatively large. Although there are coatings called nanoscale, larger particles can still be found on the final surface of the coating, and the coating surface is still rough. Reduce the size of the deposited particles of the coating and keep the process stable to avoid the appearance of larger abnormal particles, which will become