In the hole processing operation, high-speed steel twist drills are still widely used, but the gap between the processing precision and processing efficiency of various enterprises has gradually widened. The material of the high-speed cutting bit is mainly made of ceramic-coated cemented carbide. For example, when MAZAK and Mori Seiki manufacture the cast iron, the ceramic coated drill bit is used. In the processing of colored materials such as aluminum alloys, diamond-coated carbide drills, DLC coated carbide drills or drill bits with diamond sintered body teeth may be used. In short, many new high-speed cutting bits will be developed in the future.
Among various coated drill bits, ceramic coated carbide drills pay special attention to wear resistance, heat resistance and lubricity. The coating process also adopts multi-layer coating methods, such as using TiAlN, TiN, TiCN and other composite nitrogen. The compound forms a composite coating structure. The general trend of the cutting conditions of the drill bit is high speed, and the cutting speed can reach 200-300 m/min respectively depending on the material to be processed. High-speed drill cutting is a trend of high-speed and large-feeding, similar to the development trend of ball-end end mill cutting conditions. Cutting practice shows that increasing the cutting speed is beneficial to the rationalization of the chip shape and improving the roughness of the machined surface. It is expected to develop along the direction of high-speed cutting in the future; increasing the feed rate is very beneficial for chip breaking and tool life extension. In the future, it will continue to develop along the direction of the big feed.
At present, high-speed hole processing mostly uses a machining center with a spindle with a liquid supply hole, which is advantageous for improving the cutting speed of the drill bit. For example, when machining a shallow hole on a S45C material with a φ10mm coated carbide drill, the cutting speed can reach 250m/min and the feed rate can reach 1600mm/min (equivalent to 0.2mm/r). Under this condition, processing It takes only about 1 second for one hole. Hitachi Seiki Co., Ltd. and Brass Industries Co., Ltd. use this condition for shallow hole processing. Under this condition, the Brass company uses a diamond-coated carbide drill to machine small diameter holes on the aluminum alloy rod. One hole can be completed in about 0.2 to 0.5 seconds. It is expected that the small-diameter hole processing will enter the high-speed machining period of one hole for one second.
High-speed cutting has many factors affecting the life of the drill bit, such as blade wear due to high cutting heat. Cutting vibration will cause chipping, chip entanglement, and even breakage of the drill bit. In order to reduce the impact of the above faults on the life of the drill bit, the following technical measures can be taken:
(1) It is suitable for tool materials with high wear resistance and suitable for high-speed drilling, such as coated carbide.
(2) Select the shape of the cutting edge that is suitable for high-speed cutting, such as determining the appropriate drill angle and edge chamfering. Generally, the drill tip angle can be selected from 130° to 140°, which can effectively reduce the cutting torque. In addition, the cross-shaped grinding or the like can be adopted to minimize the contact area between the cutting edge and the cut surface. At the same time, the runout accuracy of the shank and the cutting edge portion and the height accuracy of the flange portion should be maximized.
(3) Select the fixture with high clamping rigidity and high vibration accuracy, and reduce the weight of the fixture to facilitate quick operation. For example, the hot-fit structure of the HSK tool holder is currently the ideal clamping system.
(4) In high-speed drilling, in order to improve the edge cooling and chip removal effect, the liquid supply method of directly supplying the coolant to the cutting edge can be used to obtain a stable cutting effect. In the coolant, in addition to the cutting fluid, a small amount of vegetable oil and air may be added to form a mixed mist-like coolant.
3 development indexable drill movements <br> <br> indexable drill is a tool as the cutting edge of the blade can be replaced, as compared with conventional drill bits, its larger diameter, but recently has developed a small φ10mm Indexable drill bit. At present, indexable drill bits have been serialized and can cover almost all types of products in the integrated drill series. Drill blades are generally made of coated cemented carbide materials, and only a few products use sintered high speed steel, diamond sintered body, CBN sintered body and other materials. Indexable drills usually have only one blade or two blades, namely the center tooth and the outer tooth. When machining large diameter holes, the drill can be installed with more than 2 blades. A drill with a single insert is similar to an integral drill with a triangular shape at the tip to reduce cutting resistance; the insert has a chipbreaker for easy chip breaking. The method of clamping the blade varies from manufacturer to manufacturer. In most cases, the blade is fastened with one or several screws. When there are more than 2 blades, the shape of the blade and the shape of the chip breaker are different. This trend is particularly evident recently. At the beginning of the development of indexable drill bits, only holes with a depth of about 3 times the diameter of the drill can be processed. At present, deep holes capable of processing 5D to 8D (D is the diameter of the drill) have been developed. The use of indexable drill bits is most effective when machining parts with uniform hole sizes. For example, by using a multi-blade drill bit, it is possible to perform chamfering and boring at the entrance of the hole at the same time, which is extremely advantageous for improving the hole processing efficiency.
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