The development trend of modern tool coating techn

Development trend of modern tool coating technology

almost all metal cutting processes benefit from coating technology. Innovations in substrate selection, coating design, pre coating and post coating preparation technology have greatly improved the performance of cutting tools and continuously expanded the limit range of metal cutting

no matter how high the evaluation is, we cannot overestimate the impact of thin-film wear-resistant coating on the tool industry and the benefits it brings to tool users. So far, the invention of chemical vapor deposition (CVD) thin film wear-resistant coating has a history of nearly 40 years, and the advent of physical vapor deposition (PVD) thin film wear-resistant coating has also been 25 years. They have played an irreplaceable key role in improving the performance of various cutting tools

this paper will review the evolution of tool coating technology in the past 40 years, analyze CVD coating technology, CVD and PVD diamond film coating technology, the impact of nanotechnology on tool coating, the preparation of tool substrate before and after coating, and the development of coating post-treatment technology

stefan gyllengahm, a senior turning technology expert of Sandvik Coromant company, commented: "modern coatings can enhance the efficiency of almost all tool materials and cutting processing. Coatings can not only improve the wear resistance of tools, but also protect tools from the cutting heat caused by high cutting speed."

mark Greenfield, global material technology director of Kennametal, pointed out that the challenge faced by tool suppliers is to continuously improve the processing efficiency and reliability of tools. At the same time, they must also meet the processing needs of various new workpiece materials (such as high hardness, high wear-resistant materials, which have greater abrasiveness to tools). For example, the high silicon aluminum alloy used to manufacture some automobile parts and the high-grade stainless steel used to manufacture medical parts have put forward special requirements for machining tools. In the processing of various workpiece materials, efficient and reliable cutting tools must be the coordinated combination of tool matrix, tool geometry and tool surface treatment

the first CVD coating technology

Dennis Quinto, technical director of the coating center of Oerlikon Balzers coating in the United States, pointed out that the CVD coating introduced in the late 1960s has brought great changes to cutting tools. By the early 1980s, CVD coatings had developed into multi-layer coatings composed of tic, TiCN and Al2O3. "Al will eventually produce 210000 tons/year of low-density polyethylene, 100000 tons/year of EVA, 35000 tons/year of ultra-high molecular weight polyethylene, 430000 tons/year of pp-icp/rcp. the annual coal consumption of the project is about 4.7 million tons. 2O3 has always been the most important coating for high-speed and high-temperature cutting, and its status has not been surpassed so far." He said, "the PVD coating technology with low deposition temperature appeared in the 1980s. Due to some obvious advantages, it can replace the CVD coating with the same composition - except Al2O3." The traditional CVD process has a higher deposition temperature (1000 ~ 1100 ℃), which may damage the heat sensitive tool materials, while the PVD process has a deposition temperature of only 180 ~ 480 ℃, which means that the non-human factor warranty within 2.1 years means that PVD can be applied to a wider range of matrix materials than CVD (New CVD processes, such as mtcvd, can also deposit coatings at lower temperatures)

new progress of CVD coating technology

Quinto of Balzers USA said that although it has not attracted much attention, CVD coating has made important technical progress in recent years, including:

(1) using medium temperature CVD (mtcvd) technology, it can deposit a thickness of 20 on cemented carbide blades μ M TiCN and Al2O3 multi-layer thick coatings are used for high-speed cutting of highly abrasive workpieces. The thickness of this kind of coating is almost twice that of traditional CVD coating, which provides better wear resistance and longer tool life

(2) through more accurate control of CVD al3o2 nucleation process, such as the use of environmental friendly foaming agent, the coating can achieve the desired α or κ Crystalline phase. The reason for this is that in several al3o2 crystalline phases that can be deposited by CVD, α- Al3o2 is the most stable, and its high temperature resistance and wear resistance are also the best

brian Hoefler, product development manager of valenite LLC, said that process expansion improved the quality of CVD coatings. "Nowadays, the deposition furnace control technology based on PC has greatly benefited the tool coating process. Tool manufacturers can obtain accurate coating thickness, uniform adhesion strength and various bright colors by accurately controlling the coating temperature and atmosphere distribution. The difference in coating thickness between production batches has been reduced by about 50% on average compared with 10 years ago."

in addition, Greenfield said that the blade brand launched by Kennametal company adopts a matrix with better deformation resistance and toughness, which is combined with a new CVD coating with a high wear-resistant oxide layer, which can make the processing efficiency higher, the tool life longer, and the downtime assistance time shorter

even seemingly insignificant factors such as coating color can play an important role in improving tool performance. Please support the inconvenience brought by valenit to our customers. Hoefler of E company pointed out that the use of color blades has become a trend in the tool market, and the coating color can also increase the use value of tools. He said, "based on the user's feedback on efficient tools, we have launched a black gray two-color coating brand specially developed for the automotive manufacturing industry. The gray coating on the back surface can enable the operator to see the used cutting edge in the common working environment with insufficient lighting in automotive manufacturers. The black coating on the front surface has an ultra smooth surface, which can reduce the failure of the blade due to bonding and wear."

research results of CVD diamond coating

after years of research in Colleges and enterprises, the production of diamond film coating by CVD process became a reality in 1994. At the IMTS exhibition that year, several major tool manufacturers announced this exciting news at the new product launch. Since then, this coating technology has made great progress in product quality and economy

in recent years, diamond film coatings have also made some important developments. Roger bollier, President of diamond tool coating, said, "although the coating material we use is still 100% artificial polycrystalline diamond with all the characteristics of natural diamond, our coating products have developed from the single-layer PCD coating initially produced in 2001 to the multi-layer nanocrystalline diamond coating produced today." Multilayer nanocrystalline diamond enhances the fracture toughness of the coating, and the fine particle structure of submicron grains makes the surface of the cutting edge of the tool smoother and the surface finish of the workpiece processed better, bollier said. "Because each layer of the multi-layer diamond coating can act as a barrier to prevent the further diffusion of cracks in the coating, its crack resistance is better, so that the coating has higher strength, and helps to improve the retention of the coating on the cutting edge, because when cutting difficult materials or intermittent cutting, the cutting edge needs to withstand severe mechanical impact."

the development of PVD coating technology

PVD coating has successfully replaced some CVD coatings since it came out 25 years ago. Due to the low temperature of PVD process, it can be applied to heat sensitive tool materials such as high speed steel. PVD process also expands the range of coated tools. Nowadays, PVD and CVD coating processes have good complementarity, and each has its own key application fields of tool coating. People also often use cvd/pvd composite coating process to deposit the bottom coating (which can be multi-layer) with CVD process, and deposit a smoother and more detailed top coating (which can also be multi-layer) with PVD process

in recent years, the development hotspots of PVD coatings mainly focus on new structural components, nanostructured coatings and PVD Al2O3 coatings. Quinto of Balzers said that the AlTiN coating produced by PVD process is known as the "second best coating" after Al2O3. But until recently, the commercial scale production of Al2O3 coating can only be realized by CVD process. Preparing this kind of non-conductive alumina coating is a challenge for PVD process, because it has been proved that it is very difficult to deposit the correct coating structure by PVD process

Horsfall of ionbond pointed out that PVD coated tools containing silicon and other materials and using new nano material preparation technology have excellent performance and can be competent for high-speed cutting (including dry or quasi dry cutting) of new high-performance machine tools

although various PVD coatings have been introduced over the years to compete with traditional CVD coatings, PVD Al2O3 coating has always been an exception due to the above deposition process problems. Not long ago, German Walter Ag exhibited PVD Al2O3 coated cemented carbide blades for processing high hardness and high abrasive workpiece materials at the 2005 emo exhibition in Hannover

new nanostructure coating

there are various statements about nanotechnology products (whose material size is below 100nm), including both rational discussion and deceptive publicity. In fact, many CVD and PVD film coatings have reached the "nano" level, because their thickness is 1 ~ 10 μ M. However, new instruments and equipment with higher resolution enable people to better measure and control nanoscale grains with smaller sizes

the key factor of adopting nano coating technology is the performance of the product, not the scale of the product. Therefore, the nano coating technology should not be regarded as just a size range. It is more important to find the critical point that can make the coating characteristics mutate. This change in characteristics can significantly improve the coating performance. For example, it can eliminate the internal defects that will become the failure mechanism of tool coating, and these failure mechanisms will lead to coating cracking and tool stress

for example, Kennametal has developed a PVD TiAlN coated blade with "nano grains",