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 status quo and development trend of foreign thread cutters are discussed in six aspects of tool materials, surface coatings, variety specifications, processing equipment, product quality and marketing techniques of thread cutters, and it is hoped to benefit domestic counterparts.
1, tool materials
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. The performance indexes such as bending strength, wear resistance and hot hardness can be increased by 2 to 3 times compared with 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 drop by 300-400 HV; if the hardness of the tool is reduced 59 ~ 60HRC, will basically lose the ability to cut. 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 types of taps with only coolant input holes, and the minimum size is only φ3mm. When such a tap is used, the cooling lubricant is directly sprayed to the cutting zone through the cooling hole. By lowering the temperature of the cutting zone, the formation of the knife blade can be effectively prevented, and at the same time, the chip is easily discharged from the chip flute with the coolant; since the chip is cooled, Reduce the temperature effect on the workpiece and improve the quality of the surface being machined. 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 approximately 30% for straight grooves, 40% for spiral grooves, 20% for screw tips, and 10% for extrusion.
Developed countries not only pay attention to the development of new products for thread cutters, but also vigorously research and develop new processes for thread processing, such as: 1 rolling two-roller method with tapered, trapezoidal (including multi-head) threads and special threads; 2 using axial rolling heads and Automatic thread rolling machine automatically rolls M5～M60 external thread on hollow blank with wall thickness of 0.8～3mm; 3 high efficiency, high precision, multi-function MC planetary tap, which can be controlled by three axes of machining center at the same time, the tap of the same pitch can be Threads of different diameters are processed, the chips are small and easy to remove, and the adjustment of the machining size can be automatically performed by the NC program.
4, processing equipment
With the rapid development and wide application of microelectronics technology and computer technology, the manufacturing technology and equipment level of foreign thread cutters have undergone tremendous changes and improvement in the past decade. For example, the whole grinding process has been widely used in the manufacture of taps, and advanced shapes such as high-speed grinding, high-pressure cooling, automatic operation and automatic loading and unloading have been used to shape the tap shape once, and the production efficiency has been greatly improved. The fast point grinding cylindrical grinding machine produced by JUNKER of Germany adopts cubic boron nitride (CBN) grinding wheel, which can complete the first grinding including the tap tip, the blade, the neck and the handle in just 6 seconds. Need to grind the square head, just add 0.5 seconds to complete). The company also produces high-speed, high-efficiency NC and CNC grinding machines that can grind, sharpen, and grind threads. The 520CNC grinder processes a M10 tap thread in just 20 seconds. The RGB25CNC thread grinder manufactured by REISHAVER in Switzerland can directly program various taps on the machine tool, or can be connected with the computer of the design center. According to the instructions of the design center, various taps can be processed, which greatly improves the "small batch, multi-variety, short cycle. "Flexible production capacity, the delivery cycle is generally only one week, special tools can be delivered within 2-3 days. Japan's OSG has dozens of tap thread grinding machines manufactured by JUNKER, Germany; EMUGE Germany has 14 GBA machines and several RGB2510 machines manufactured by Swiss REISHAVER. On the one hand, foreign thread cutter manufacturers attach great importance to the introduction of high-precision equipment with high processing efficiency, high degree of automation and lack of domestically in key processes (generally 3% to 5% of all equipment); Relying on technological advancement, we develop technological equipment with unique characteristics. By developing high-efficiency special equipment, computer technology is applied to special equipment, and the automation degree of special equipment is improved to meet the requirements of simple operation, convenient adjustment, and stable product quality. At the same time, the efficiency of imported equipment is maximized, and many foreign threads are used. Tool manufacturers have world-class craftsmanship and equipment. For example, Japan's OSG's self-made special equipment accounts for about 60% of all equipment, which can well meet the special needs of developing new products.
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After entering the 21st century, the development of high-speed cutting technology and factory automation and intelligent processing technology puts higher demands on thread cutters. At present, foreign countries have mass-produced machining centers with spindle speeds of 2000 to 3500 r/min, but the cutting capacity of the matching tools cannot meet the requirements of these advanced equipment. Therefore, it is necessary to speed up the development and development of threaded tools (including tool materials, structural types, geometric parameters, etc.) so that "each tool is adjusted to suit each specific object." Special attention should be paid to the development of super-hard tool materials and tool surface coating technology to improve the cutting performance of threaded tools and improve their service life to meet the needs of high-speed cutting. Factory automation and unmanned machining require tooling products with high reliability, long tool life and good chip evacuation structure, as well as high quality stability and cutting edge repeatability. In addition, in order to meet the needs of the future development of the machinery manufacturing industry, it is necessary to develop a thread cutter identification system, an online monitoring system, and a comprehensive management system for tool transportation, sharpening, and adjustment.
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