Thread cutters are special tools for machining various internal and external threads. They are widely used in the field of machining and require a large amount of demand. Thread cutters play an important role in the international tool market. Thread cutter sales in developed countries such as the United States, Germany, and Japan account for about 25% of total tool sales, second only to twist drills (about 30%). In recent years, with the change of cutting processing conditions and the importance of high productivity, higher requirements have been placed on the material, surface treatment and structural parameters of thread cutters. Understanding the current status and development trend of foreign thread cutters is of positive significance for China's thread cutter manufacturers to adjust product structure, improve product levels, and actively participate in market competition. In this paper, the current situation and development trend of foreign thread cutters are discussed in six aspects of tool materials, surface coatings, variety specifications and processing equipment of thread cutters, and it is hoped to benefit domestic counterparts.
1, tool material
Most of the industrial thread cutters are made of high-speed steel. Thread cutters made of alloy tool steel are usually limited to household use. For example, more than 82% of the taps produced by German GUHRING Precision Tools Co., Ltd. are made of high-performance high-speed steel materials, about 6% are made of hard alloy, about 8% are made of powder metallurgy high-speed steel; only about 4% of total tap output is used. Taps are also made in large quantities from ordinary high speed steel, and alloy tool steels are rarely used. More than 90% of the company's discs are made of ordinary high-speed steel, and the rest are made of high-performance high-speed steel. About 50% of the thread cutters from Japan's OSG and Germany's EMUGE are made of high-speed steel, and the other 50% are high-quality, high-quality, high-quality steel, such as powder metallurgy, cobalt, high-speed steel. Material manufacturing. In the thread processing of difficult-to-machine materials and hard-material workpieces, powder metallurgy cobalt high-speed steel tool materials are receiving more and more attention, and their flexural strength, wear resistance, thermal hardness and other performance indexes can be increased by 2 to 3 times than ordinary cobalt-containing high-speed steel. However, due to the high processing cost of powder metallurgy high-speed steel, it is currently not widely used in the selection of thread cutters.
2, surface coating
After the surface coating of the high-speed steel thread cutter, the cutting friction can be effectively reduced, the tool wear can be reduced, and the cutting performance and service life of the tool can be greatly improved (generally, the tool life can be increased by 2 to 3 times). At present, TiN coating and composite coating processes have been widely used in the production of foreign thread cutters. For example, various coating products of German GUHRINR and EMUGE have accounted for about 40% of their thread cutter production.
Hardness is one of the important parameters for the cutting performance of high speed steel thread cutters. During the machining of the thread, a high heat of cutting is generated and transmitted to the tool, which reduces the hardness of the tool. According to the relevant information, when the temperature of the cutting zone exceeds 550 °C, the metallographic structure of the tool will change, resulting in a rapid decrease in the hardness of the tool; for every 100 °C increase in temperature, the hardness can be reduced by 300~400 HV; if the hardness of the tool is reduced 59~60HRC will basically lose the cutting ability. The surface hardness of threaded cutters can be significantly increased after coating: TiN coating hardness can reach more than 2300HV; TiCN coating hardness can reach 3000HV or more. The surface coatings of threaded tools have their own characteristics and have different application scopes: TiCN coated high speed steel thread cutters have higher hardness and can achieve cutting performance comparable to uncoated cemented carbide tools; in addition, in some For cutting applications, TiCN coated high speed steel cones offer lower cost advantages than uncoated cemented carbide tools. Tool life can be increased by more than 10 times when tapping a brass plate or cast aluminum workpiece with a TiCN coated tap; tool life can be increased by 4 times when tapping a gray cast iron or hypereutectoid aluminum workpiece with a TiAlN coated tap the above. Compared to TiN coatings, TiAIN coatings provide higher hardness and better oxidation resistance, so TiAIN coated tools are more suitable for high speed machining.
3, variety specifications
In order to meet the needs of thread processing of different materials, different types and different precisions, foreign thread cutter manufacturers have continuously improved tool structure and geometric parameters and developed a large number of new products. Taking a tap as an example, there are a blade taper tap which can change the direction of chip discharge, a spiral groove tap, an extrusion tap which does not generate chips, a center hole tap which can be sprayed or an internal cooling function, and a chip-capable content. Chip taps, hexagonal neck taps with anti-break function, high-precision broaching taps, combined taps with guide Post taps and front end with drilled reamers, etc., are available in a wide variety of functions and functions. There are more than 20 kinds of taps with only the coolant input hole, and the minimum specification is only φ3mm. When such a tap is used, the cooling lubricant is directly sprayed to the cutting area through the cooling hole, and the knife can be effectively prevented by lowering the temperature of the cutting zone. The formation of the tumor, at the same time facilitates the discharge of the chips from the chip flute with the cooling liquid; as the chips are cooled, the temperature influence on the workpiece can be reduced, and the quality of the surface to be processed can be improved. By using such taps to machine difficult-to-cut materials, the service life of the tap can be more than doubled. According to the 1998 EMUGE product sample statistics, EMUGE's total number of thread cutters is nearly 100,000. There are more than 200 varieties (different materials, different types) and specifications (different pitches and dimensions) of M6 taps, M6. There are more than 50 varieties of die specifications. The number of different structural taps manufactured abroad is about 30% for straight grooves, 40% for spiral grooves, 20% for screw tips, and 10% for extrusion.
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