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2. Development of vacuum coating technology
The vacuum coating technology has not been developed for a long time. It was not until the 1960s that CVD (chemical vapor deposition) technology was applied to cemented carbide tools. Because this technology needs to be carried out at a high temperature (process temperature is higher than 1000oC), the type of coating is single, and the limitations are very large. Therefore, the initial stage of development is not satisfactory.
By the end of the 1970s, PVD (Physical Vapor Deposition) technology began to emerge, creating a new world with a bright future for vacuum coating. After a short period of 20-30 years, PVD coating technology developed rapidly. The reason for this is that because it forms a film in a vacuum-sealed cavity, it has almost no environmental pollution problems and is environmentally friendly; because it can obtain a bright, luxurious surface, there are seven colors, silver, and transparent colors in color. , golden yellow, black, and any color between gold and black, can be described as colorful, can meet the various needs of decorative; and due to PVD technology, you can easily get high hardness and high resistance that are difficult to obtain with other methods. The abrasive ceramic coatings and composite coatings are applied on tooling and molds, which can double lifespan and achieve low cost and high yield. In addition, PVD coating technology has low temperature and high energy. Features, can be formed on almost any substrate, therefore, the application is very broad, and its development is not surprising. Vacuum coating technology has developed to new technologies such as PCVD (Physical Vapor Deposition) and MT-CVD (Medium Temperature Chemical Vapor Deposition). Various coating equipments and various coating processes emerge one after another and are now in this field. Has shown a hundred flowers, hundreds of contending gratifying scenes.
At the same time, we should also clearly see that the development of vacuum coating technology is again seriously unbalanced. Due to the extremely harsh working environment of the tools and molds, the film adhesion requirements are much higher than the decorative coatings. Thus, although manufacturers of decorative coatings have spread all over the country, there are not many manufacturers capable of producing mold coatings. In addition, the lack of after-sales service for tools and die coatings has made it impossible for most domestic coating equipment manufacturers to provide complete tool coating technology (including pretreatment, coating, post-coating, and inspection). Technology, coated tooling, mold application technology, etc.) Moreover, it requires process technicians to have a solid metal material and heat treatment knowledge in addition to the expertise of the master coating, pretreatment of the mold coating front surface. Reasonable selection of knowledge, tool, mold coating, and technical requirements for use on the machine, if any problems occur, will give users a conclusion that the use effect is not ideal. All these have severely restricted the application of this technology to tools and molds.
On the other hand, because this technology is an emerging edge discipline in materials science, physics, electronics, chemistry and other disciplines, it has been applied to a few key manufacturers in the field of tool and mold production in China. Most of them are also taking the path of introducing advanced equipment and technology from abroad, and they still need a process of digestion and absorption. Therefore, the current domestic technological forces in this field are not commensurate with their development, and they urgently need to catch up.
3. The basic concept and characteristics of PVD coating
PVD is an abbreviation of English "Physical Vapor Deposition", which means physical vapor deposition. We now commonly refer to vacuum deposition, sputtering, ion plating, and the like as physical vapor deposition.
The more mature PVD methods are mainly multi-arc and magnetron sputtering. Multi-arc plating equipment is simple in structure and easy to operate. Its ion evaporation source can be operated by the power supply of the welding machine. The arc striking process is also similar to the welding. Specifically, under a certain process pressure, the arcing needle is briefly contacted with the evaporation ion source, and the gas is discharged. . Since the cause of multi-arc plating is mainly due to the continuous movement of the arc spot, a molten pool is continuously formed on the surface of the evaporation source. After the metal is evaporated, it is deposited on the substrate to obtain a thin film layer. Compared with the magnetron sputtering, Not only has a high utilization of the target, but also has a high ionization rate of metal ions, the advantages of strong binding between the film and the substrate. In addition, the color of multi-arc coating is relatively stable. Especially when TiN coating is applied, the same stable golden yellow is easily obtained in each batch, making the magnetron sputtering method unmatched. The disadvantage of multi-arc plating is that under the condition of low temperature coating with a conventional DC power supply, when the coating thickness reaches 0.3 μm, the deposition rate and reflectance are close to each other, and film formation becomes very difficult. Moreover, the surface of the film begins to change. Another inadequacy of multi-arc plating is that since the metal is evaporated after melting, the deposited particles are large, the density is low, and the wear resistance is inferior to that of magnetron sputtering.
Visible, multi-arc coating and magnetron sputtering coating have their own advantages and disadvantages, in order to play their respective advantages as much as possible, to achieve complementarity, the multi-arc technology and magnetron technology into a coating machine came into being . A multi-arc plating process has appeared in the process, then the magnetron sputtering method is used to thicken the coating, and finally a new method of multi-arc coating is used to achieve the final stable surface coating color.
In the mid-late and late decades of the 1980s, hot cathode electron gun evaporation ionization and hot cathode arc magnetron plasma coating machines emerged. The application effect was very good, and TiN coated tools quickly gained popularity. The hot cathode electron gun evaporation ion plating uses copper crucible to heat and melt the metal material to be plated. The xenon filament is used to heat and degas the workpiece, and the electron gun is used to enhance the ionization rate. A TiN coating with a thickness of 3 to 5 μm can be obtained not only, but also a combination thereof. Force and wear resistance are both good performance, even with the grinding method are difficult to remove. But these devices are only suitable for TiN coating, or pure metal film. For multi-layer coating or composite coating, the force is not satisfactory, and it is difficult to adapt to the requirements of high-speed cutting of high-hardness materials and variety of mold applications.
Currently, some developed countries (such as German CemeCon, UK ART-TEER, and Swiss Platit) replace the original DC power supply and pulse with a non-equilibrium magnetic field instead of the original balanced magnetic field and 50 KHz IF power on the basis of the traditional magnetron sputtering principle. The power source replaces the conventional DC bias voltage, and the auxiliary anode technology is used to make the magnetron sputtering technology mature gradually. It has been applied in large quantities on the mold coating. Now the coatings that have been stably produced mainly include TiAlN, AlTiN, TiB2, and DLC. , CrN, China's Guangdong, Jiangsu, Guizhou, Zhuzhou and other places have also gradually introduced such equipment, there is a great momentum of fire.
4. 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 obtaining part, vacuum measuring part, Power supply part, process gas input system, mechanical transmission part, heating and temperature measurement part, ion evaporation or sputtering source, water cooling system and other parts.
4.1 Vacuum chamber
Coating equipment mainly consists of continuous coating production line and single-room coating machine. Because of the high requirements of the mold coating on the heating and mechanical transmission parts, and the shape and size of the mold, the continuous coating production line is usually difficult to meet. A single chamber coater is required.
4.2 Vacuum Obtained Section
In the vacuum technology, the vacuum acquisition part is an important part. Due to the high adhesion requirements of the coating, the background vacuum level before the coating process starts is preferably higher than 6 mPa, and the vacuum level after the coating process is even higher than 0.06 mPa. Therefore, a vacuum is selected to obtain a high level of equipment. The degree of vacuum is very important.
For now, there is no pump that can operate from atmospheric pressure until it approaches ultra-high vacuum. Therefore, the availability of vacuum is not achievable by vacuum equipment and methods. Several pumps must be used in combination, such as mechanical pumps and molecular pump systems.
4.3 Vacuum Measurement Section
The vacuum measurement part of the vacuum system is to measure the pressure in the vacuum chamber. Like a vacuum pump, there is no vacuum gauge that can measure the entire vacuum range. People then make many kinds of vacuum gauges according to different principles and requirements.
4.4 Power Supply Section
The target power supply mainly includes DC power supply (such as MDX) and intermediate frequency power supply (such as PE, PEII, and PINACAL produced by American AE Company); the workpiece itself usually needs to be supplied with DC power (such as MDX) and pulse power (such as PINACAL+ produced by American AE company). Or RF power.
4.5 Process Gas Input System
Process gases, such as Ar, Kr, N2, acetylene, CH4, H2, O2, etc. 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 piping is simple and clear, and it is easy to repair or replace the cylinder. Each coating machine does not affect each other. There are also cases where multiple coaters share a group of cylinders, which may be a chance to see in some of the larger coating shops. Its advantage is that it reduces the consumption of gas cylinders, and makes unified planning and layout. The disadvantage is that due to the increase in joints, the chance of leakage increases. Moreover, the coating machines will interfere with each other, and the air leakage of the tubes of a coating machine may affect the product quality of other coating machines. In addition, when replacing the cylinders, it must be ensured that all the mainframes are in a non-use state.
4.6 The tool coating of the mechanical transmission part requires that the perimeter must be uniform in thickness. Therefore, there must be three rotations in the coating process to meet the requirements. That is, while a large workpiece table rotation (I) is required, a small workpiece carrying table also rotates (II), and the workpiece itself can rotate at the same time (III).
In the mechanical design, it is generally a large driving gear in the center of the bottom of the large workpiece turntable, surrounded by a small number of star wheels to mesh with it, and then use the shift fork to toggle the workpiece to rotate. Of course, when the mold coating is done, generally two rotations are sufficient, but the load capacity of the gear must be greatly enhanced.
4.7 Heating and Temperature Measurement Section
When making a mold coating, how to ensure the uniform heating of the plated workpiece is much more important than the heating of the decorative coating. The mold coating equipment generally has two heaters before and after, and the thermocouple is used to measure and control the temperature. However, due to the different settings of the thermocouple clamp, the temperature reading cannot be the true temperature of the workpiece. There are many ways to measure the true temperature of a workpiece. Here is a simple Surface Thermomeer. The working principle of the thermometer is that when the thermometer is heated, the spring on the bottom will be heated to expand, so that the pointer will push the positioning pointer to rotate until the maximum temperature. When the temperature is lowered, the spring shrinks and the pointer rotates in the reverse direction, but the positioning pointer remains at the highest temperature position. After the door is opened, the temperature indicated by the positioning pointer is read, that is, the highest position of the surface thermometer when the vacuum chamber is heated. Temperature value.
4.8 Ion evaporation and sputtering source
The multi-arc plated evaporation source is generally a round cake, commonly known as a round cake target. In recent years, a rectangular multi-arc target has also appeared, but no obvious effect has been observed. The round cake target is mounted on a copper target (cathode seat) and the two are ribbed. There is a magnet in the target seat. By moving the magnet back and forth to change the magnetic field strength, the speed and trajectory of the arc spot can be adjusted. In order to reduce the temperature of the target and the target seat, cooling water is continuously supplied to the target seat. In order to ensure high electrical and thermal conductivity between the target and the target holder, tin (Sn) gaskets can also be added between the target and the target holder.
Magnetron sputtering coating generally uses rectangular or cylindrical targets.
4.9 Water Cooling System
Because the mold coating, in order to increase the atomization rate of metal atoms, each cathode target as much as possible with a large power output, requires adequate cooling; In addition, the mold coating of many kinds of coatings, the heating temperature is 400~500oC, therefore, it is also very important to cool the vacuum chamber wall and each sealing surface. Therefore, the cooling water is preferably supplied from a chiller of about 18 to 20oC.
In order to prevent the low-temperature vacuum chamber wall and cathode target from coming into contact with hot air after the door is opened, the water cooling system should be capable of switching to the hot water supply state about 10 minutes before the door is opened. The hot water temperature is about 40~45oC.
5. Work steps for tooling PVD
The basic process flow of the tooling and die PVD can be briefly described as follows: IQC → pre-processing → PVD → FQC.
5.1 IQC
The main work of IQC (In Quality Control) is to check whether the drawing is consistent with the actual object, in addition to the regular inventory quantity. It is also necessary to carefully inspect the surface of the workpiece, in particular whether there are any defects such as cracks on the cutting edge. Sometimes, the edge of some cutters and granules is observed under the stereomicroscope, which makes it more convenient to find problems. In addition, IQC personnel should also pay attention to the presence of plastic, low-melting-point solder, etc. in the coated parts. Mixed with the coating process, it will be seriously deflated in the vacuum chamber, the light will cause the entire batch of products to be decoated, and the heavy one will cause the original OK product to be scrapped, resulting in disastrous consequences.
5.2 Pretreatment Process (Steam Gun, Sandblasting, Polishing, Cleaning)
The purpose of the pretreatment is to clean or roughen the surface of the workpiece. Purification is to remove all kinds of surface contaminants and prepare a clean surface. Various scavengers are usually used for purification by means of mechanical, physical or chemical methods.
Coarsening is contrary to photo-etching in that its purpose is to prepare a rough surface to increase the structural strength of the sprayed coating or paint decoration.
The main methods we now have are: high-temperature steaming, washing, sandblasting, grinding, polishing and other methods.
5.2.1 Steaming at high temperature
At present, the high temperature steaming equipment commonly used in PVD workshops is steam guns. Its maximum operating temperature is 145?C, and its pressure is about 3 to 5 bar. Because the mold often has some small holes, threaded holes, often in the hole oil, residual coolant and other impurities, the use of conventional cleaning methods difficult to remove. At this point, the high-temperature steaming equipment can maximize its superiority.
5.2.2 Cleaning
The pre-cleaning procedure for mold coating of various plants is roughly as follows:
1. Ultrasonic wave removal → 2. Over water → 3. Ultrasonic degreasing → 4. Over water → 5. Ultrasonic self-change → 6. Overwater → 7. Overpure water → 8. Strong wind drying
In the specific implementation, there are many differences from the cleaning before we are familiar with the decorative coating. This is because the substrate of the decorative coating is mostly stainless steel or titanium alloy and it is not easy to rust. In addition, decorative coatings are absolutely impermissible for watermarks, defects, and the like. Therefore, the decorative coating has a very high water quality requirement, even reaching 15 MΩ or more. To ensure that the high quality of the cleaning can be obtained by repeated cleaning and soaking in high-quality pure water plus ultrasonic waves for a long time. However, the mold cleaning is different, especially some hot die steels. If it is cleaned like a decorative coating, it will rust.
Due to the original surface state of the mold coating, in addition to some high standard mirror molds, it is generally rougher than the decorative coating. Therefore, the requirements for the surface state after the coating are not as high as the decorative coating. This allows We use fast water, dry with dry, oil-free compressed air, and then treat the molds with strong air to dry them. Those high-standard mirror molds are generally 136 stainless steel and can be cleaned by a decorative coating.
In a word, the cleaning method before the mold coating is different for the materials used in the mold, and varies according to the surface state before the mold coating, and can not be the same. The following is a ranking of several materials rust from hard to easy for reference:
Stainless steel, hard alloy, cermet alloy, DC53, HSS, 8407 There is an automatic cleaning machine model CR288, produced in Germany. The maximum cleaning capacity of the machine is 80KG. It is mainly used for cleaning tools, small parts, or small-size molds. It has a total of three cleaning cylinders, the inside of the solution are tap water + cleaning agent, tap water, deionized water. In addition to the common ultrasonic, flushing, spraying, swinging, hot air drying and other functions, another advantage of this machine is that it has a vacuum step at the end to make the moisture evaporate as soon as possible.
Ten processes of the automatic washing machine memory are preset by the supplier. One to nine can be used for the purification of different types of products and different surface conditions. The tenth kind is used to add cleaning agent.
5.2.3 Sandblasting
The sand blasting method uses compressed air to force the abrasive to flush the surface of the workpiece to remove surface defects such as rust, carbon deposition, welding slag, oxide scale, residual salt, and old paint. According to the conditions of abrasive use, sandblasting can be divided into two types: dry blasting and wet blasting.
The sandblasting process parameters mainly include gun distance, tilt angle, rotation speed of the clamping table, moving speed, stroke, round-trip times, sand blasting time, and blast pressure. The parameters we have used include: gun spacing: 30~70mm; tilt angle 30~70?C; clamping table rotation speed 10~30; round trip frequency 3~9 times; blast pressure: 1.8~3.5 bar. During the specific operation, the upper and lower limits are selected according to factors such as the degree of contamination of the workpiece surface, the hardness of the workpiece, and the geometry of the workpiece surface. The abrasive used in the dry blasting machine is glass beads, suitable for spraying some materials in hardness medium, such as oil steel, mold, etc.; the abrasive used in the liquid blasting machine is alumina, which has high hardness and is suitable for Spray some hard material, such as carbide. For mold coating, the abrasive grain size used for sandblasting is also important. If the abrasive grain size is too large, the workpiece surface is too rough; if the abrasive grain size is too small, it will reduce the impact strength, and even embedded in the workpiece surface, cleaning is difficult to remove, so that the workpiece coating adhesion is reduced. For this reason, in some countries in Europe, the abrasive grain size used for sand blasting prior to the coating of the dies was carefully studied. It must be ensured that more than 85% of the grain size can be used within the two points A and B. In contrast, China's abrasive suppliers still lack consensus in this regard, and we rarely do tests in this area.
5.3 PVD coating process (heating, ion cleaning, coating, cooling, process gas, gas pressure, temperature, sputtering power)
5.4 FQC
The English spelling of FQC is "Function Quality Control", which means function quality control, which is different from OQC (Out Quality Control) in a general sense. The contents of FQC mainly include appearance inspection, depth inspection, adhesion inspection, wear resistance inspection, corrosion resistance inspection, and simulation test. The main applications currently applied in our factory are appearance inspection, depth inspection and adhesion inspection.
Since most of the products we are in contact with are not allowed to perform destructive inspections, we will place batches of samples with each lot during coating. When doing depth inspection and adhesion inspection, in most cases, it is actually the inspection of batch samples. Because the sample and the product are difficult to be consistent in terms of raw materials, heat treatment status, and clamping position, the results thus detected will have a certain error with the actual product value. Sometimes there may be considerable errors that can only be used as a reference. Of course, when necessary, we can also create accurate simulations to achieve accurate measurements.
5.4.1 Visual Inspection
For the product after the door is opened, the surface should be carefully inspected for defects such as cracks, loose coatings, and looseness. For the cutters and the cutters, they must also be carefully examined under the microscope.
5.4.2 Depth inspection
Layer depth inspections include metallographic inspection methods, X-ray inspection methods, optical tests using a monochromatic light source, and ball mill test methods. The depth inspection of the mold coating was performed on a ball mill. The method is to first use a steel ball with a diameter of 10mm to be ground with the test surface, and then measure the relevant data of the wear scar under the microscope and bring it into the formula to easily calculate the depth of the layer.
This layer depth inspection method is characterized by: it is convenient to apply, and the error is slightly larger. However, this error will not be too great when applied to the mold. Interested colleagues can also refer to the relevant instructions.
There are many inspection methods for adhesion, and each company has developed corresponding testing methods based on the characteristics of its products. Among them, there are two authoritative methods, one is Rockwell hardness tester, indentation test with a conical diamond indenter, observation under the microscope, to determine the adhesion of the coating with the number of cracks around the indentation High and low. This method is very demanding on the shape of the diamond indenter. It not only strictly requires that the center point be in the center of the circle, but also the roundness of the diamond cone must be very regular. Unfortunately, at present, China still does not have its national or industrial standards; the other method is the scratch method. Some coatings in our country have initiated earlier research departments and are also adopting this method. There are special national industry standards available. Inquire.
6. Treatment of fixtures
7. Coating process (blasting, grease coating technology)
8. Detection Technology (Coupling Force Detection, Layer Depth Detection, Etching)
9. Coating stripping technology (TiN/TiAlN stripping technology, CrN/DLC/CrAlTiN stripping technology, carbide surface stripping technology)
10. Applied Technology of Coated Tools (Correct Selection of Coat, Correct Use of Coated Tools
The optimization of the coating on the tool is very large. Because the high-speed cutting process has higher temperature than the traditional cutting process, applying the coating can exert its high-temperature resistance, oxidation resistance, and hardened material. For example, a chromium nitride (CrN) coating can reduce the coefficient of friction, improve finish and chip removal.
Tooling PVD coating technology
1. Summary