Development status of tool shanks for the hottest

2022-09-23
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The development status of tool shanks for high-speed machining

metal cutting has entered a new development stage represented by high-speed cutting. Because high-speed cutting can greatly improve the cutting rate of materials and the processing quality of parts, and reduce processing costs, it has become one of the development directions of metal cutting today. High speed cutting tool technology is a key technology of high-speed machining, which includes high-speed cutting tool material, tool handle system, tool system dynamic balance technology, tool monitoring technology and so on. This paper gives an overview of the development of tool shanks for high-speed machining

1. Requirements of high-speed cutting on tool system

the so-called tool system refers to a complete tool system composed of tool handle, collet and cutting tool. The tool handle is connected with the spindle of the machine tool, and the cutting tool is loaded into the tool handle through the collet. To enable the tool system to carry out cutting at high speed, the following basic conditions should be met:

higher system accuracy

system accuracy includes system positioning and clamping accuracy and tool repeated positioning accuracy. The former refers to the connection accuracy between the tool and the tool handle, and between the tool handle and the machine tool spindle; The latter refers to the consistency of tool system accuracy after each tool change. The tool system has high system accuracy, which can ensure the static and dynamic stability of the tool system under the condition of high-speed machining

higher system stiffness

the static and dynamic stiffness of the tool system is an important factor affecting the machining accuracy and cutting performance. The insufficient rigidity of the tool system will lead to the vibration of the tool system, which will reduce the machining accuracy, aggravate the wear of the tool and reduce the service life of the tool

good dynamic balance

under the condition of high-speed cutting, the imbalance of small mass will cause huge centrifugal force and cause sharp vibration of machine tool in the process of machining. Therefore, the dynamic balance of high-speed tool system is very important

2. Problems in the structure of traditional solid long tool shanks

at present, the traditional tool shanks used in CNC milling machines, CNC boring machines and machining centers are standard 7:24 taper solid long tool shanks. The connection between the tool handle and the spindle of the machine tool is only positioned by the conical surface, and there is a large gap between the end face of the spindle and the flange end face of the tool handle. This kind of tool handle structure will have the following problems under the condition of high-speed cutting:

the dynamic and static stiffness of the tool is low

when the tool rotates at high speed, due to the action of centrifugal force, the spindle taper hole and the tool handle will expand radially, and the amount of expansion will increase with the increase of rotation radius and speed. This will cause the expansion of the tool handle to be less than that of the taper hole of the spindle, resulting in a fit gap, which will further reduce the stiffness of the low rigid connection that was originally combined only by the taper

poor dynamic balance

the standard 7:24 taper handle is long, so it is difficult to achieve full-length gapless fitting. Generally, it is only required to fit with more than 70% of the front section, and there is often a certain gap in the rear section. This gap will cause the radial circular runout of the tool and affect the dynamic balance of the tool system

low accuracy of repeated positioning

when the ATC (automatic tool changing) method is used to install the tool, it is difficult to ensure the consistency of the combination of the tool handle and the spindle taper after each tool change due to the long taper. At the same time, the long knife handle also limits the high speed of the tool change process

3. Development and application of a variety of new tool shanks

in order to meet the requirements of high-speed machining on the tool system, various industrial developed countries have developed a variety of new structure tool shanks in recent 10 years. The introduction is as follows

1) HSK tool holder

hsk (German hohlschaftkegel abbreviation) tool holder is a double-sided clamping tool holder developed by the machine tool Research Institute of Aachen University of technology in Germany in the early 1990s. It is the most representative of double-sided clamping tool holders. HSK knife handle has been listed in the German DIN standard in 1996 and became the international standard iso12164 in December 2001. Because its stiffness and repeated positioning accuracy are several to dozens of times higher than the standard 7:24 taper handle, it has been widely recognized and adopted in the machinery manufacturing industry. For example, in German Mercedes Benz and Volkswagen, HSK tool holders are widely used in milling, drilling and turning. In the engine and driver production line of FAW Volkswagen, more than 250 CNC machine tools have adopted HSK high-speed short cone hollow handle tool system, with a total of 6 specifications

according to the research, the HSK tool handle is positioned on both sides by the conical surface (radial) and the flange end face (axial), realizing the rigid connection with the spindle, as shown in Figure 1. When the tool handle is installed on the spindle of the machine tool, the hollow short taper handle can fully contact the taper hole of the spindle and play a centering role. At this time, there is still a gap of about 0.1mm between the HSK tool handle flange and the spindle end face. Under the action of the tensioning mechanism, the right movement of the pull rod causes the conical surface at the front end of the pull rod to expand the elastic gripper radially. At the same time, the outer conical surface of the gripper acts on the 30 ° conical surface of the inner hole of the hollow short conical handle. The hollow short conical handle produces elastic deformation and makes its end face close to the end face of the main shaft, realizing the function of simultaneous positioning and clamping of the tool handle, the conical surface of the main shaft and the end face of the main shaft

Fig. 1 connection structure and working principle of HSK tool handle and spindle

the main advantages of this tool handle structure are:

effectively improve the combination stiffness of tool handle and machine tool spindle. Due to the over positioning combination of conical surface and end face, the effective contact area between the tool handle and the main shaft is increased, and the double-sided positioning is carried out from the radial and axial directions, which greatly improves the combined stiffness of the tool handle and the main shaft, and overcomes the weakness of the technical conditions of Rockwell hardness tester (table 2-1) that the stiffness of the traditional standard 7:24 conical handle is insufficient when rotating at high speed

it has high repeated positioning accuracy and fast automatic tool change action, which is conducive to the realization of high-speed ATC. Due to the 1:10 taper, the length of the cone is short (about half of the similar specification of the 7:24 taper handle). After each tool change, the contact area between the tool handle and the spindle is consistent, so the repeated positioning accuracy of the tool handle is improved. Due to the hollow structure, it is light in weight and convenient for automatic tool change

it has good high-speed locking performance. The tool handle and the spindle are locked by the elastic expansion claw. The higher the speed is, the greater the centrifugal force of the expansion claw is, and the greater the locking force is

according to the provisions of German DIN standard, HSK tool handle adopts balanced design, and its structural forms include a, B, C, D, e and F6 types, each type is corrosion-resistant and has a variety of sizes. A. Type B is the tool holder for automatic tool change, type C and D are the tool holders for manual tool change, and type E and F are keyless connections, which are suitable for tool holders for ultra-high speed cutting

2) km knife handle

km knife handle is a 1:10 short cone hollow handle coexisting with HSK knife handle, which was jointly developed by Kennametal company of the United States and widia company of Germany in 1987. Its structure is shown in Figure 2. Km tool holder first proposed the principle of double-sided positioning of end face and cone. Km tool handle adopts a 1:10 short taper fit, with a short fitting length, which is only 1/3 of the length of the standard 7:04 taper handle with similar specifications, partially solving the interference problem caused by the simultaneous positioning of the end face and the taper. On the other hand, the fit interference between KM tool handle and spindle taper hole is high, which can reach 2 ~ 5 times of HSK tool handle structure, and its connection stiffness is higher than HSK tool handle. At the same time, compared with other types of hollow taper shank connection, the taper shank diameter used for the same flange outer diameter is smaller, so the spindle taper hole expands less when rotating at high speed, and the high-speed performance is good

Figure 2 connection structure between KM tool handle and spindle

3) problems existing in HSK tool handle and KM tool handle

due to the use of double-sided positioning, the tool handle has been positioned in the inner hole of the spindle. To realize over positioning well, it requires that the conical surface of the tool handle and the end face of the flange have high shape accuracy and mutual position accuracy, which increases the difficulty of the manufacturing of the tool handle. Therefore, the manufacturing cost of this type of tool handle is high, and its price is usually 1.5 ~ 2 times that of the conventional standard 7:24 taper handle

it is incompatible with the traditional spindle end structure and tool handle, and cannot be directly used in traditional machine tools, so it is necessary to redesign the spindle end of machine tools. Of course, at present, the spindle end of high-speed machine tools produced by many foreign machine tool manufacturers is directly designed with the tool handle of hollow short cone structure. For example, at the 8th China International Machine Tool Exhibition held in Beijing in April 2003, almost all high-speed machine tools adopted HSK tool handles

the material requirements for manufacturing tool handles are high. Due to the over positioning of this tool handle, its heating deformation is required to be small and uniform, otherwise the original positioning accuracy will be destroyed, and it is not easy to load and unload

4) BIG-PLUS tool handle

research and modification of tool handle for high-speed machining in addition to Germany and the United States, some Japanese companies are also committed to improving the original 7:24 solid long taper handle in various forms, in order to achieve double-sided positioning, improve positioning accuracy and continue to expand business stiffness in China in the future, such as the 3lock system taper handle of Japanese Nikken company, BIG-PLUS precision taper handle of big daishowa Seiki company and Showa d-f-c knife handle developed by Shenghe Jingji Co., Ltd. These tool handles have been improved on the basis of the original standard 7:24 taper handle

the taper of BIG-PLUS tool handle is still 7:24. Its working principle is that the clearance of the end face is small before the tool handle is installed into the taper hole of the main shaft and locked. After locking, the elastic expansion of the inner hole of the spindle is used to compensate the end clearance, so that the end face of the tool handle is close to the end face of the spindle, thereby increasing its stiffness. This kind of tool handle also adopts over positioning, so its shape accuracy and position accuracy must be strictly controlled, and its manufacturing process is more difficult than HSK tool handle

this improved taper handle can be used interchangeably with the original 7:24 taper handle and can be applied to the taper hole of the original spindle. However, in order to meet the development requirements of further high-speed machine speed, 1:10 short cone hollow handle has a more promising future. Therefore, more Japanese companies still actively adopt German DIN standard HSK knife handles, such as NT tool company, Kuroda Seiko, Shenghe Seiji, Mitsubishi metal, etc., which have successively introduced HSK production technology

to sum up, the development trend of tool holders for high-speed machining is to adopt the principle of double-sided over positioning to improve the combined stiffness of tool holder system. At the same time, solve the related problems caused by the over positioning of the tool handle, and constantly improve the performance of the tool handle material

4. Research on high-speed cutting tools in China

the research on high-speed cutting technology in China started late. In the early 1990s, Beijing University of technology began to study the basic theories and methods of high-speed cutting. At the same time, Guangdong University of technology, Shandong University, Chengdu Tool Research Institute and other universities and scientific research institutions have also carried out research on high-speed cutting related technologies, such as high-power high-speed spindle unit, high-speed cutting tools, ceramic rolling bearings. However, there is a big gap between China and foreign countries in the overall level of high-speed cutting technology research. In terms of high-speed cutting tool technology, Shandong University of technology and Chengdu Tool Research Institute have done a lot of work and made some achievements. But so far, China has not independently developed a practical high-speed cutting tool, and even all enterprises applying high-speed cutting technology in China, almost all high-speed cutting tools must be imported from abroad. For example, the high-speed cutting tools used in the production lines of FAW Volkswagen Jetta, Audi car engine and driver parts are imported products (from 49 foreign companies). It can be seen that how to realize the comprehensive localization and commercialization of high-speed cutting tool system to reduce tool costs is the key to improve the international competitiveness of automotive and other electromechanical products in China

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