Method to improve the effect of coating tool
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The choice of tool material depends on the cutting conditions and also on the wide range of surfaces to be re-ground. For example, if the front surface of the tool is re-ground, it is more advantageous to use cobalt-containing high-speed steel, which is more resistant to crescent wear after the front surface of the tool is uncoated. The progress of tool materials, the emergence of high-speed steel, hard alloy, toughened ceramics, cobalt fund ceramics, polycrystalline diamond and CBN and other material tools, the use of metal cutting efficiency has been greatly improved. Each material has its own advantages and disadvantages, so it has a specific purpose.
A new requirement of tool geometry is put forward for coated tool. It is generally believed that the improvement of tool geometry, such as the front Angle, chip space, etc., should focus on chip removal ability, in order to adapt to the increase in cutting amount at a higher feed and a higher speed. Coating knife has higher machining efficiency, it allows a higher feed and cutting speed (can be increased to the original cutting speed of 2 ~ 3 times). For hard - working materials, coating improves tool performance greatly.
The reason why the tool with superhard coating wears out less is that the film superhard compound has high hardness, high melting point and excellent thermochemical stability. Superhard compounds are mostly composed of nitrides carbides and borides of transition metals. They're bonded by strong covalent bonds; With a very low standard free energy of formation, it forms a very stable system, and the hardness does not decrease significantly at high temperature. These films show higher resistance to mechanical wear and heat resistance wear than carbide and high speed steel and other tool materials.
Coating conditions, process parameters, pre-treatment of the substrate before plating and so on are very important for the preparation of high-quality coating. The state of the tool surface is critical to the adhesion of the coating. The surface of the coated workpiece must be free from other film layers, burn spots, rust spots, oil stains or other stains. The workpiece should be cleaned by strict sandblasting and degreasing and ion bombardment before the hard film is grown in vacuum.
The tool of different coating material, use effect is different. Low speed cutting, TiC coating has the advantage; High speed cutting, TiN is more suitable; HfN has higher thermochemical stability than TiN and is suitable for working at higher cutting speeds. TiN and Al2O3 coating, high speed cutting Al2O3 coating has a significant advantage, and low speed cutting TiN coating tool life longer.
Tool life and film thickness also have a certain relationship. If the tool surface wear is the benchmark in the future, the tool life will increase with the increase of the film thickness, but the film thickness reaches saturation at 5um, that is, the life is no longer significantly increased; However, if the depth of crescent depression on the cutter surface was the benchmark of tool life before, the tool life was proportional to the thickness of the film, and no saturation observation was found. When the film layer is too thick, it is easy to cause peeling. Now, the coating thickness of turning tool is mostly 5 ~ 10um on one side.
The influence of film thickness on the hard coating of milling cutter is different. When milling steel workpiece, no matter what kind of film layer is used, the tool life is the longest when the film thickness is about 2um, but the life decreases when the film thickness increases again. However, for cast iron with less impact, the optimum film thickness changes to a thicker direction. TiC coatings have the best results in milling, while Al2O3 coatings show no advantage in turning.
Carbide tools are usually coated by CVD method, but PVD coating treatment almost does not cause a decline in edge strength, PVD coated carbide milling cutter is more durable than CVD coating. For the wear resistance of general HSS tools, CVD coating is superior to PVD coating, but the precision, complex shape, expensive and non-regrinding HSS tools are mostly PVD coating. It is a rather complicated technology to improve the effect of coating tool and give full play to the function of hard coating. In order to achieve the optimal combination, the establishment of coating tool database, for different workpieces, through the computer selection of tool coating materials and processing parameters, the situation becomes simple and effective, so as to truly achieve the quality, efficiency, low cost of the target of processing.