Surface modification of the hottest tools

2022-08-07
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Tool surface modification

the improvement of tool development technology has led to more and more applications of high-efficiency cutting materials through such strict test comparison and systematic analysis. This continuous technological development has increased the efficiency of cutting tools by about 30 times in the 20th century. CVD thin coating and PVD coating can greatly improve the surface properties of cutting tools. Up to now, this effect is far from exhausted. Using modern analysis technology, the microstructure of the tool surface can be clearly observed, and its remarkable optimization effect can be accurately recognized

in the past, the surface structure of the tool was realized through predetermined process procedures. Now, the function design can be carried out according to the optimal tool performance

the purpose of surface modification is to improve the surface friction conditions, so as to improve the tool life or machining efficiency, improve the tool wear resistance, reduce the friction heat and reduce the wear. The most commonly used surface modification method is the surface coating of materials. Through the compounding of carbides, nitrides and oxides of high hardness metals, the properties of single compounds can be adjusted, especially in improving the ability of wear resistance, oxidation resistance, diffusion wear and bonding wear. Of course, introducing other materials into the surface (such as injection method) can also have a lasting impact on the surface properties of materials

the adhesion mechanism between chip and tool is mainly friction except mechanical occlusion. The friction properties can be effectively improved by a material modification method - depositing a soft coating on the tool surface

in addition, the surface morphology can be modified, such as polishing or purposeful roughening (to form lubricating oil grooves). Polishing is a traditional method to reduce friction by mechanical means, especially for cutting tools that do not add lubricant to the cutting area. Polishing is an effective method to reduce friction in most cases

periodic surface structure can be formed by polishing. Structural elements of a certain shape can also be obtained by lithography or laser. Compared with sheet metal processing, these methods are not common in cutting processing at present. A theoretical basis of this method is that microstructure can reduce the heat transfer between the chip and the tool, and reduce the thermal load of the tool

polishing of PVD coating

polishing process belongs to the modification of surface morphology. There are various polishing methods for ground or coated surfaces. In addition to Truva polishing method used for large quantities of parts, there are brush method and sand blasting method commonly used in tool production. These methods are not novel and have been used in the production of cutting blades for many years, such as the cauliflower like surface structure for polishing CVD thick coatings. The polished cutting insert shows very uniform wear after 6 minutes of cutting. The unpolished blade shows parallel micro cracks, which will lead to the rapid widening of the wear band and make it inconvenient for the tool to take and place the sample in advance

these polishing methods are now also often used for PVD coatings. For example, on the surface of a PVD coated hole machining blade, a structure called "droplet" in the PVD arc method can be seen. These droplets act like stones in the river bed, hindering the chip removal process, which is particularly unfavorable in hole machining. If the chips can be removed quickly and with less friction, the chemical fiber company in Japan between the chips and the tool will not do so. The contact time will be reduced and the heat transferred to the tool will also be reduced. Unimpeded chip removal reduces the cutting force, and avoids the bite and blockage of chips in the drill bit and milling cutter groove. The quality of polishing depends on the selection of polishing method and the adjustment of process parameters. Do not apply lubricating grease and dustproof grease

the advantages of the polishing process are obvious. Let's take an example of a fried dough twist drill. A measuring instrument developed for final inspection can measure the friction in the chip groove. The reduction of friction is related to the surface condition. The friction coefficient of polished bit groove is only 25% of that of unpolished bit groove. The treated bit allows for higher cutting and drilling depth. In addition, more stable chip removal also extends tool life

surface macro treatment process

surface polishing avoids the running in effect that may adversely affect the tool performance. The research shows that the whole carbide tool is in the "running in" state during the first 10 drilling, and the feed force is almost half. The polished tool shows very good performance as if there is no "running in". In order to ensure the performance of the cutting tool, this surface treatment is absolutely necessary in dry cutting. However, even in the traditional wet cutting, the tool life can be significantly prolonged and the cutting is more reliable through appropriate surface polishing

most of the ground surfaces present a periodic structure with typical grinding traces. If the coating is carried out immediately, this shape will remain. However, since the processes that will affect the surface, such as edge rounding (mostly by sandblasting or brushing) or coating pretreatment, are necessary, the grinding surface must be modified. The correct operation of these processes can have beneficial effects. The transverse grinding trace along the chip discharge direction will adversely affect the chip discharge. It should be leveled to obtain a macroscopically smooth surface. In this way, the pretreated surface can be polished again after coating, which is simpler and more effective. (end)

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