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Evolving tool coating technology
A variety of new tool coatings are becoming popular, featuring multi-layer coatings and new coating materials for specific processing needs to optimize processability. Fred Teeter, chairman of the Surface Engineering Coatings Association (SECA) in Amherst, New York, and executive director of Teeter Consulting, said: "Anything with wear can be considered for thin-film ceramic coatings." Applications such as turbine engine parts are growing, but coatings still account for the vast majority of applications on cutting tools. The coating does prove its value. According to SECA, the life of coated tools can be increased by 2-10 times compared to non-coated tools. New coatings with ever-increasing operating temperatures and hardness continue to emerge, and some specific properties of the coating (such as wear resistance, toughness, etc.) are constantly improving. Titanium nitride (TiN) coatings used to be the first choice for thin film coatings decades ago. Although this familiar golden yellow coating is still used today, a variety of new coatings have emerged. The combined application of multi-layer coatings can achieve a balanced performance, which is difficult to achieve with a single layer coating. With the emergence of new thin film coatings, many engineers may now face the problem of too many (and not too few) types of coatings to choose from. Mahesh Sukumaran, general manager of Eifeler Coating Services, Canada, stated, “In the past 5-10 years, the shortening of preparation time has led to a significant reduction in coating costs. In addition, the use of multi-layer coatings can give full play to the advantages of different coatings, thus Reducing the need for lubricants.†In evaluating the overall trend of tool coatings, he explained that there are still many users who have consulted him about TiN coatings. They don’t know that there are many new coatings available. select. Eifeler offers nine different PVD coatings (Figure 1), both standard TiN coatings and ZrN, TiCN and AlTiSiN coatings. Exxtral Plus is one of the most popular coatings. It is a multi-layer coating consisting of AlTiN+AlTiCrN. It is suitable for carbide end mills and can process hardened steel at high speed in semi-dry or dry cutting. The coating has a heat resistance threshold of up to 800 ° C and a Vickers hardness of HV 3500 ± 500. Sukumaran pointed out that the main challenge for coating technology is to improve the adhesion of certain coatings and further reduce the thickness of the coating. The general coating is not lubricious, and our multi-layer coating combines lubricity and wear resistance to reduce friction between the tool and the workpiece, thereby reducing or eliminating the use of lubricating fluids. Get a better chip flow. A noteworthy trend in tool coatings is that their applications are becoming more specialized. Christopher Halter, manager of coatings and surface technology supplier Oerlikon Balzers, also noticed this. The company currently offers 24 different coating products, of which Balinit Alcrona is an AlCrN coating and is the last general-purpose coating grade developed by the company. Halter noted that a variety of new specialty coatings (such as the Balinit Aldura coating for hardened tool steels with a hardness greater than HRC50) represent a future trend. Another AlCr-based coating, Balinit Helica, is specifically designed for twist drills. The Balinit Aldura grade is a layer of AlCrN-based functional coating deposited on the supporting TiAlN coating. The TiAlN layer ensures good adhesion and mechanical strength, while the AlCrN layer provides excellent thermoset and oxidation resistance (up to 1100 °C) and isolates the tool from the heat of cutting. Oerlikon Balzers has developed a new coating technology, P3e (Pulse Enhanced Electron Emission Technology), which will be of great interest to tool engineers. Using this technology, the first time you can use the PVD process to prepare Al2O3-based coatings with high hardness and good thermal and chemical stability. Since the deposition temperature is lower than 600 °C, the tool with fine grained carbide substrate can also be used. The coating is applied without deformation. For the first time, P3e technology was applied to the “X3turn†coated grade of Oerlikon Balzers, which achieved good test results for turning. Under dry cutting conditions, X3turn's performance is comparable to conventional CVD coated insert grades. This coating can also be used very well in the processing of interrupted cutting and the use of coolant. Now, all fine-grained and ultrafine-grained carbide substrates can be coated with α-Al2O3-based coatings at deposition temperatures below 600 °C, and the thermodynamic properties of the deposition process are very stable and do not deform the tool. Halter expects that the new P3e technology will open up new applications and increase the productivity of users using turning and milling inserts. Platt, Switzerland, is a company that sells coating equipment to tool companies and has extensive experience in coating technology. Platit's PVD coating equipment has been developed and manufactured using a number of patented technologies that can be used not only for conventional, nano- and gradient coatings, but also for nanocomposite coatings. The nano-coating is actually just a thinner multi-layer coating with a thickness of less than 20 nm per layer. The hardness of the coating depends on the total thickness of the alternately applied coating. The number of layers in the coating can reach hundreds. Floor. The nanocomposite coating is composed of a typical coating (such as TiAlN) embedded in the Si3N4 amorphous matrix. The nanocomposite structure can improve the hardness and lubrication of the coating and increase the maximum working temperature of the coating. Platit also manufactures a patented three-layer coating consisting of a tie layer, an intermediate layer (single or gradient structure) and a nanocomposite top layer for superior anti-friction and toughness. For example, the nACo3 three-layer coating is TiN as the bottom layer, AlTiN as the intermediate layer, and the nACo nanocomposite coating as the top layer. The nACo itself is a nanocomposite coating composed of TiAlN embedded in a Si3N4M amorphous matrix. According to data provided by Platit, the coating has a hardness of 38–45 GPa and a maximum operating temperature of 1200 °C. The company's coating equipment uses the traditional magnetron cathode arc principle (ARC) and patented technologies for side-rotating cathode (LARC) and center-rotating cathode (CERC). The company offers 29 different coatings, and the coating equipment is available in standard configurations with three “base†coatings (ie TiN, TiCN and TiAlN). According to the company, these three coatings currently account for more than 80% of the world's coatings market. The company's other coatings are designed for specific applications, including 17 optional coatings, 6 nano-coatings and 3 dedicated three-layer coatings. Sherwood Bollier, president and CEO of Niagara Cutter, pointed out that the three technologies of tool design include matrix materials, coatings and tool geometries. He believes that although the new coating can improve tool performance, it is not always possible to improve tool performance without optimizing the entire tool. Bollier pointed out that “it is easier to obtain a new coating with new color, higher hardness and maximum working temperature, but what really matters is the performance of the tool. For the new coating, we check the tool performance and Adjustments are made according to the processing needs. We have found that once the coating is selected for a certain tool material and cutting edge, the preparation of the cutting edge is very important.†Niagara Tool Company specializes in round tools (such as end mills) and Its miniature end mill division) is a miniature end mill for processing medical and electronic components. Proper cutting edge preparation depends on the coating used and the material being cut. Cutting edges that work well with aluminum may not perform well when cutting cast iron. He also believes that post-coating secondary treatments (such as coating polishing) are just as important as proper tool design and edge preparation. Bollier explained, “Although the coating keeps the cutting edge sharp, the cutting edge may be too sharp. The uncoated cutting edge will have minimal wear after the initial small amount of cutting, which is beneficial for 'stabilizing' the tool and eliminating chattering. The correct cutting edge preparation method pre-processes the tool to simulate the 'stability' process of the uncoated tool during the initial cutting.†Bollier said, “We have several new coatings with very good properties, but they are suitable for specific Processing. For example, a new AlcrN coating called Alcrona, recommended by Balzers, has proven to be suitable for gear hobs and seems to be naturally applicable to end mills. “We have to work hard to make Alcrona coatings work for me. It is really suitable for the cutting edge of the tool. Once we have done enough testing and testing, we can apply Alcrona coating extensions to our processing. Niagara claims that in a specific cutting test, the coating can double the tool life of the user with a 35% increase in cutting speed and feed rate. The cutting edge of the Alcrona coated milling cutter has undergone 150 reciprocating cuttings (4,340 materials of hardness HRC30 milled on a Makino S58 milling machine, cutting speed of 1100 fpm, feed rate of 176 ipm), and substantially no built-up edge. Sandvik Coromant has a wide-ranging coating engineering team. Although the company can outsource its tool coating work, it believes that it is important to have its own coating technology and capabilities. Margareta Palsson, global manager of Sandvik's management of tool grades, believes that a complete cutting solution comes from a reasonable match between the coating and the proper matrix, geometry and edge preparation. “Every process has subtle differences, and this difference translates into a significant difference in productivity,†she says. “We are committed to fine-tuning the production process to meet these processing requirements.†Sandvik develops annually 6-8 new tool grades, some developed for new processing needs and others with improvements to existing coatings. The company believes that a comprehensive cutting test should be carried out when matching the coating to the tool. To this end, the company cuts 25,000 cutting edges per year and produces chips weighing up to 45 tons. For example, this year Sandvik launched the GC4205 grade for steel turning, which uses a TiCN/Al203 medium temperature CVD coating designed to achieve high metal removal rates at cutting edge temperatures up to 1200 °C. Stable processing of steel parts. Because of the need to choose among hundreds of cutting inserts, Sandvik Coromant recognizes that too much information puts the user overburdened. For this reason, Sandvik has adopted a method called CoroKey that allows engineers to Reduce the amount of work required to select a tool based on its specific needs. After the user selects the workpiece material type, processing type, processing conditions and cutting data, CoroKey can help them select the appropriate cutting insert. While coating is an important element for every tool, CoroKey helps engineers select the right tool by matching the workpiece material and machining method to the recommended depth of cut, feed and cutting speed. Palsson is convinced that future machining will require extensive tool performance studies, including the development of tools and coatings for new aerospace titanium alloys, composites, powder metallurgy materials, and the production of compacted graphite iron for automotive engine blocks. "In these processes, atomic structures, metal ratios, surface finishes, cutting edge preparation, and nuances in the direction of crystal alignment will all make a big difference in productivity," Palsso said. Don Graham, turning product manager at Seco Tools, said that in order to develop a new process and a new coating called DurAtomic, Seco Tools is studying the crystal structure of the coating. By tilting the crystal orientation of the CVD-Al2O3 coating, the coating can be made harder and tougher when cut. He explained, "Our crystal orientation at the atomic scale increases both the toughness of the cutting insert and the wear resistance, which are usually opposite each other. The tilt of each grain is even small. The angle can also greatly enhance its toughness. The DurAtomic coating uses TiCN as the bottom layer and the new Al2O3 as the top layer. The earlier grades (such as Seco's TP000 series) use the additional TiN as the top layer, which is no longer needed. Because Al2O3 has sufficient strength and surface finish. TP2500 is the first coating grade developed by Seco using DurAtomic technology for turning, which provides better wear resistance when used in a wide range of steel parts. And toughness. In addition, TP2500 can optimize the processing of stainless steel and cast iron, effectively processing materials from K10 to M40. Through more than 80 on-site cutting tests, TP2500 is proved to be suitable for roughing, surface finishing and finishing of various materials. Field trials have shown that the TP2500 coating also reduces cutting edge built-up edge, and the TP2500 improves productivity compared to commonly used coated tools. %, extending tool life by 40%. At the same time, the measured coating hardness increased by 11%, and the new TP2500 coating also reduced tool temperature by 3%-4%. Iscar Metals Inc. Precision carbide tools (including milling tools, hole machining tools, turning tools and cutting tools) have developed a new Sumo Tec coating technology (both for CVD and PVD). Sumo Tec coating technology is based on Based on the company's original ALTEC PVD and Alpha-Tec CVD coating technology, Mike Gadzinski, National Training Director for Iskar, said, “The most common failure mechanism for tools is chipping, so we have used a three-layer coating. Layer: TiCN is used as the underlayer, Al2O3 or AlTiN as the intermediate layer, and TiN film is used as the top layer. TiCN improves tool wear resistance to prevent chipping and the middle layer provides a thermal barrier. To improve this base coat, Iskar uses a proprietary post-treatment process to produce a smooth surface that is both heat and resistant to chipping. In cutting tests for earlier products, tool life has increased by 15%-80%. â€