The correct surface treatment (coating) of small circular tools can improve the tool life, reduce the processing cycle time and improve the surface quality. However, it may be a confusing and laborious work to correctly select the tool coating according to the processing needs. Each coating has both advantages and disadvantages in machining. If an inappropriate coating is selected, the tool life may be lower than that of uncoated tools, and sometimes even more problems than before the coating.
At present, there are many kinds of tool coatings to choose from, including PVD coating, CVD coating and composite coating alternately coated with PVD and CVD. Fulandi brand milling cutter and tungsten steel milling cutter each coated milling cutter adopts the world’s advanced Swiss PLATIT coating technology, which makes the hardness and service life of the tool more than double in cutting. It is beneficial to determine which coating to choose in machining engineering.
Hardness OF MILLING CUTTER
The high surface hardness brought by coating is one of the best ways to improve the tool life. Generally speaking, the higher the hardness of the material or surface, the longer the service life of the tool. Titanium nitride carbide (TiCN) has higher hardness than titanium nitride (TIN). Due to the increase of carbon content, the hardness of TiCN is increased by 33%, and its hardness variation range is about HV30 ~ 04000. The application of CVD diamond coating with surface hardness up to hv90 on cutting tools has been relatively mature. Compared with PVD coated tools, the service life of CVD diamond coated tools is increased by 10 ~ 20 times. The high hardness and cutting speed of diamond coating can be 2 ~ 3 times higher than that of uncoated tools, making it a good choice for cutting non-ferrous materials.
Wear resistance OF MILLING CUTTER
Wear resistance refers to the ability of the coating to resist wear. Although the hardness of some workpiece materials may not be too high, in the production process
The elements added in and the process used may cause the cutting edge of the tool to crack or blunt.
High friction coefficient will increase the cutting heat, resulting in shortened coating life and even failure. Reducing the friction coefficient can greatly prolong the tool life. The coating surface with fine and smooth or regular texture is helpful to reduce the cutting heat, because the smooth surface can quickly slide the chips away from the rake face and reduce the generation of heat. Compared with uncoated tools, coated tools with better surface lubricity can also be processed at a higher cutting speed, thus further avoiding high-temperature fusion welding with workpiece materials.
Oxidation temperature refers to the temperature at which the coating begins to decompose. The higher the oxidation temperature is, the more favorable it is for cutting at high temperature. Although the normal temperature hardness of TIA coated layer N may be lower than that of TiC coated layer N, it has been proved that it is much more effective than TiCN in high temperature processing. The reason why the coating layer N of TIA can still maintain its hardness at high temperature is that a layer of alumina can be formed between the tool and the chip, and the alumina layer can transfer heat from the tool to the workpiece or chip. Compared with high-speed steel tools, the cutting speed of cemented carbide tools is usually higher, which makes TiAlN become the coating of cemented carbide tools. Cemented carbide drills and end mills usually use this PVD TiAlN coating
Adhesion resistance OF MILLING CUTTER
The anti adhesion of the coating can prevent or reduce the chemical reaction between the tool and the processed material, and prevent the workpiece material from depositing on the tool. When machining non-ferrous metals (such as aluminum, brass, etc.), chip nodules often occur on the tool, resulting in tool breakage or workpiece size out of tolerance. Once the processed material begins to adhere to the tool, the adhesion will continue to expand. For example, when processing aluminum workpiece with forming tap, the aluminum adhered to the tap will increase after processing each hole, so that the tap diameter will become too large, causing the workpiece to be scrapped due to out of tolerance size. Coatings with good adhesion resistance can play a good role even in processing occasions with poor coolant performance or insufficient concentration.
gENERAL application of coating
Achieving cost-effective application of coatings may depend on many factors, but for each specific processing application, there is usually only one or several feasible coating options. Whether the coating and its characteristics are selected correctly may mean the difference between significantly improved processability and almost no improvement. Cutting depth, cutting speed and coolant may affect the application effect of tool coating. Because there are many variables in the processing of a workpiece material, one of the good ways to determine which coating to choose is through trial cutting.