4. Tool coating material
Coating the tool is one of the important ways to improve the performance of the tool. The emergence of coated tools has made a major breakthrough in the cutting performance of the tools. Coated tools are coated with one or more layers of refractory compounds with good wear resistance on the toughness of the tool body, which combines the tool matrix with the hard coating, thereby greatly improving the performance of the tool. Coated tools can improve processing efficiency, improve processing accuracy, extend tool life, and reduce processing costs.
About 80% of the cutting tools used in the new type of CNC machine tools use coated tools. Coated tools will be the most important tool in the field of CNC machining in the future.
⑴ Types of coated tools
According to different coating methods, coated tools can be divided into chemical vapor deposition (CVD) coated tools and physical vapor deposition (PVD) coated tools. Coated carbide tools generally use chemical vapor deposition, and the deposition temperature is about 1000 ℃. Coated high-speed steel tools generally adopt physical vapor deposition method, and the deposition temperature is about 500℃;
According to the different substrate materials of coated tools, coated tools can be divided into hard alloy coated tools, high-speed steel coated tools, and ceramic and superhard materials (diamond and cubic boron nitride) coated tools.
According to the nature of the coating material, coated tools can be divided into two categories, namely “hard” coated tools and “soft” coated tools. The main goals pursued by “hard” coated tools are high hardness and wear resistance. Its main advantages are high hardness and good wear resistance, typically TiC and TiN coatings. The goal of “soft” coated tools is a low coefficient of friction, also known as self-lubricating tools, and the friction between it and the workpiece material The coefficient is very low, only about 0.1, which can reduce bonding, reduce friction, and reduce cutting force and cutting temperature.
Recently developed nano-coated (Nanoeoating) tools. This kind of coating tool can use different combinations of multiple coating materials (such as metal/metal, metal/ceramic, ceramic/ceramic, etc.) to meet different functional and performance requirements. A reasonably designed nano-coating can make the tool material have excellent anti-friction and anti-wear functions and self-lubricating properties, which is suitable for high-speed dry cutting.
⑵ Features of coated tools
① Good mechanical and cutting performance: The coating tool combines the excellent performance of the base material and the coating material, which not only maintains the good toughness and high strength of the base, but also has the high hardness, high wear resistance and low resistance coefficient of friction of the coating. Therefore, the cutting speed of the coated tool can be increased by more than 2 times than that of the uncoated tool, and a higher feed rate is allowed. The life of coated tools has also been improved.
② Strong versatility: Coated tools have wide versatility, and the processing range is significantly expanded. One type of coated tool can replace several types of non-coated tools. ③ Coating thickness: The tool life will increase with the increase of the coating thickness, but when the coating thickness reaches saturation, the tool life will no longer increase significantly. When the coating is too thick, it is easy to cause peeling; when the coating is too thin, the wear resistance is poor.
④ Regrindability: poor regrindability of coated flute, complex coating equipment, high process requirements, and long coating time.
⑤ Coating materials: cutting tools with different coating materials have different cutting performance. For example, when cutting at low speed, TiC coating has the advantage; when cutting at high speed, TiN is more suitable.
⑶ Application of coated tools
Coated tools have great potential in the field of CNC machining and will be the most important tool variety in the field of CNC machining in the future. Coating technology has been applied to end mills, reamers, drills, composite hole machining tools, gear hobs, gear shapers, gear shaving cutters, forming broaches and various machine-clamped indexable inserts to meet the needs of high-speed cutting processing. The need for materials such as steel and cast iron, heat-resistant alloys and non-ferrous metals.