How to Correctly Choose the Coating of Carbide Cutting Tools

At present, the status of cemented carbide cutting tools and their core coating technology in CNC machine tools is getting more and more attention. The breakthrough of coating technology is also included in many topics. In order to reduce the wear of cemented carbide tools, extend the life of the drill bit, and increase the cutting speed, the tungsten carbide milling cutter is coated with a titanium aluminum nitrogen coating with high hardness and high wear resistance.

Ⅰ. What is carbide cutting tool coating

Coated cemented carbide cutting tools are obtained by coating a thin layer of refractory metal or non-metallic compound with good wear resistance on the surface of cemented carbide substrate with good strength and toughness. The coating acts as a chemical barrier and thermal barrier, reducing the diffusion and chemical reaction between the tool and the workpiece, thereby reducing the wear of the crescent socket.

Coated carbide cutting tools have the characteristics of high surface hardness, good wear resistance, stable chemical properties, heat resistance and oxidation resistance, low friction factor and low thermal conductivity. It can increase the tool life by 3 to 5 times compared with uncoated tools during cutting. Above, increase the cutting speed by 20%~70%, improve the machining accuracy, and reduce the cost of tool consumption by 20%~50%.

Therefore, carbide cutting tools have become a symbol of modern cutting tools, and the proportion of use in tools has exceeded 50%. At present, various carbide cutting tools used in cutting include turning tools, boring tools, drills, reamers, broaches, taps, thread combs, rolling heads, milling cutters, forming tools, gear hobs and inserts. Tooth knives, etc. can be coated to improve their performance.

Ⅱ. Coating methods of carbide cutting tools

At present, there are two coating methods commonly used in production including physical vapor deposition (PVD) method and chemical vapor deposition (CVD) method. The CVD method is mostly used for cemented carbide.

Chemical vapor deposition (CVD) method: The deposition temperature is 900℃~1100℃, the coating thickness can reach 5-10μm, and the equipment is simple and the coating is uniform. When the cemented carbide tool is coated by CVD method, due to its high deposition temperature, a brittle decarburization layer (η phase) is easily formed between the coating and the substrate, resulting in brittle fracture of the blade.

In the past ten years, with the progress of coating technology, the PVD method can also be used for cemented carbide. The combined PVD/CVD composite coating process is called the PACVD method (plasma chemical vapor deposition method). That is, plasma is used to promote the chemical reaction, and the coating temperature can be reduced to below 400℃ (the current coating temperature can be reduced to 180℃~200℃), so that there will be no diffusion between the cemented carbide tool and the coating material. Phase change or exchange reaction can maintain the original toughness of the blade. According to reports, this method is particularly effective for coating diamond and cubic boron nitride (CBN) superhard coatings.

When coating by CVD method, the cutting edge needs to be passivated in advance, so the cutting edge is not as sharp as the uncoated blade. Therefore, the PVD method should be used for hard alloy tools that produce thin chips and require sharp cutting edges for finishing. In addition to coating on ordinary cutting inserts, the coating can also be coated on integral cutting tools, and it has been developed to be coated on welded carbide cutting tools. According to reports, a company has adopted the PCVD method on welded carbide drill bits. As a result, the life of the drill bit when processing steel materials is 10 times longer than that of high-speed steel drill bits, and the efficiency is increased by 5 times.