The selection of tool materials depends on the cutting conditions and the regrinding surface. For example, if the rake face of the tool is reground, the use of cobalt-containing high-speed steel is more advantageous, because it is more resistant to crater wear after the rake face of the tool is uncoated. With the advancement of tool materials, the use of high-speed steels, hard alloys, various toughening ceramics, cobalt-based cermets, polycrystalline diamond, and CBN tools has emerged, greatly improving the machining efficiency of metal cutting.
It is generally believed that the improvement of tool geometry, such as rake angle and chip removal space, should be focused on chip removal capacity, so as to adapt to increase of cutting volume at higher feed rate and higher speed. The coating cutters has high machining efficiency, which allows higher feed rate and cutting speed (up to 2~3 times the original cutting speed). For difficult-to-process materials, the coating improves the performance of the tool greatly.
The tool wear with super hard coating is low because the high hardness of the film super hard compound, the melting point is high, and the thermo chemical stability is excellent. The super hard compounds are mostly made up of nitrides, carbides and borides of transition metals. They are combined with strong covalent bond and have a very low standard generation free energy, which constitute a very stable system, and the hardness cannot reduce at high temperatures. The coatings show higher mechanical wear resistance and heat-resistant wear than hard alloy and high speed steel tool materials.
The coating conditions, process parameters and pre-coating pretreatment are very important for the preparation of high quality coatings. The state of tool surface is crucial to the adhesion of the coating and workpiece surface to be plated must be free of other layers, burns, rust, oil, or other contamination. The workpiece should be strictly sandblasting and degreasing, and the ion bombardment is also needed cleaning before the hard film is grown in the vacuum.
Different coating materials for cutting tools, the use effect is different. For low speed cutting, the TiC coating has the advantage. TiN is more suitable for high speed cutting, and the thermo-chemical stability of HfN is higher than that of TiN, which is suitable for working at higher cutting speed. Compared with TiN and Al2O3 coatings, the Al2O3 coating has a significant advantage in high speed cutting, while TiN coating tools have a longer service life at low speed cutting.
Carbide tools are usually coated by CVD, but PVD plating hardly causes edge strength reduction, and PVD coated carbide milling cutters are more durable than CVD coatings. For general goods of high speed steel cutters wear resistance of CVD coating, PVD coating is better than that, but the high-speed steel cutting tool precision, complex shape, and high price cannot be re grinding for PVD coating. It is a rather complicated technique to improve the use effect of coating tool and give full play to the effect of hard coating. In order to achieve the optimal combination, the database of coated tool database is established. It is simple and effective to select different tools and coating materials and processing parameters for different parts, so as to achieve the goal of high quality, high efficiency and low cost.