　　 Abstract: The tool system refers to the coupling system of the machine tool spindle (or tool holder) and the tool, including the spindle (or tool holder), the tool holder (and the device for coupling the tool holder on the tool holder) and the clamping mechanism, and the tool holder It is the last link of the machine tool and the tool, which plays an important role in the performance of the entire tool system. In this paper, the four tool systems HSK, KM, BIG-plus and Capto, which are used more and more representative at home and abroad, are compared and analyzed. Their structural characteristics and applications are introduced, and their advantages and disadvantages are compared. The selection of each is given, which provides a reference for the selection of actual processing.
High-speed machining is a high-tech processing technology integrating materials science, engineering mechanics, mechanical dynamics and manufacturing science. It has been widely used in many industries such as automobile manufacturing, aerospace and mechanical processing. It is understood that 40% of high-speed machining comes from high-speed milling, and in high-speed milling, the performance of the tool system will greatly affect the processing quality and processing efficiency. Therefore, the research and development of high-speed milling tool systems has attracted the attention of mechanical engineering experts and scholars at home and abroad. Therefore, this paper analyzes the characteristics of the following four typical tool systems and their selection in high-speed milling.
HSK tool system features and selection
1. Features of the HSK tool system
The HSK tool system is shown in Figure 1a. Its structural features are hollow, thin wall and short cone with a taper of 1:10, using an externally expanding clamping mechanism from the inside to the outside. The positioning in the main shaft is over-positioned, and the end surface and the tapered surface are simultaneously positioned and clamped, as shown in Fig. 1b. When clamping, due to the interference of the taper, the tapered surface is elastically deformed by pressing, and the shank moves axially to the spindle taper hole to eliminate the initial gap and achieve the fit between the end faces, thus achieving double-sided Synchronous clamping.
2. Selection of HSK tool system
In high-speed milling, it is important to select the HSK tool holder correctly and reasonably according to the machining requirements. The HSK tool holders are divided into six types: A, B, C, D, E and F. When selecting the model and specifications of the HSK tool holder, the main considerations include: the maximum speed of the spindle, the structural characteristics of the tool holder and the bearing capacity. , the popularity of tools and accessories, etc.
(1) Choice of tool holder model. According to the structural characteristics of the HSK shank, the A and B shanks are mainly used for medium and high speed machining with automatic tool changer; the C and D shanks are mainly used for medium and high speed machining with manual tool change; The F-type shank is suitable for ultra-high-speed machining because it has a symmetrical structure without any grooves and slits and has good dynamic balance.
Domestic use of Type A and Type C standards in DIN 6989b-1, such as HSK50A, HSK63A and HSK100A. HSK50 and HSK63 holders have spindle speeds of up to 25 000 r/min, HSK100 holders up to 12 000 r/min, and precision balanced HSK holders with spindle speeds of up to 40 000 r/min. However, as the speed increases, the radial stiffness will decrease.
(2) Choice of tool holder specifications. When selecting the HSK shank specification, the bearing capacity of the shank (including the ultimate bending moment and the ultimate torque) should be considered. The bending moment and torque generated by the cutting force during actual machining should be selected according to the critical bending moment and torque value of the shank. .
When approaching the critical point, the joint strength is insufficient, although the flange face of the shank remains in full contact with the end face of the spindle, but the bending moment is close to the critical value separating the two. The magnitude of this critical moment is mainly determined by the tension, so increasing the tension can increase the maximum bending moment. This has special significance for tools with a long overhang, but increasing the tension increases the total load acting on the clamping ramp. This is especially true when using high speeds, due to the centrifugal force, although the clamping force exerted by the internal jaws increases, so that the reliability of the clamping is improved, but on the other hand the shank is made The thinnest part is subjected to a large load, causing damage to the shank. The relevant manual can be consulted to make the specific selection of the tool holder. The specification distribution of the HSK tool holder is shown in Table 1.
The six specifications of the HSK tool system and its application are shown in Table 2.
KM tool system features and selection
1. Features of the KM tool system
The KM tool system is shown in Figure 2. It also uses a 1:10 hollow short cone fit and double-sided positioning. It has the advantages of high rigidity, high precision, quick clamping and easy maintenance. Its dynamic stiffness is higher than the HSK tool system. The KM tool holder is locked with a steel ball bevel, as shown in Figure 3. When clamping, the steel ball is pushed out along the inclined surface of the groove of the rod, and is clamped on the inclined surface of the locking hole on the shank to tighten the shank toward the spindle hole. The shank is elastically deformed so that the end surface of the shank is in close contact with the end surface of the main shaft.
2. Selection of KM tool system
The standard KM holders are available in six models: KM32, KM40, KM50, KM63, KM80 and KM100. The research shows that compared with the HSK tool system, the KM tool holder/spindle has a larger radial interference, which is 2~5 times that of the HSK. The clamping force and locking force of the KM tool holder are significantly larger than the HSK tool holder. Because of the large locking force, the coupling rigidity of the shank/spindle is strong, so the performance of the KM tool system is optimal in the BT tool system, the HSK tool system and the KM tool system. Their structure and performance comparison are shown in Table 3.
Table 3 Comparison of KM holder, HSK and BT holder
In addition, the KM tool system itself supports tools with central internal cooling. As long as the tool and the machine have a central internal cooling channel, the KM tool system provides the possibility to allow the cutting fluid to smoothly reach the cutting area of ​​the tool, thus providing further tool performance. Protection. However, due to patent protection, the KM tool system has been promoted and applied only on certain types of machine tools in the United States and Japan, and not much domestically.
Features and selection of BIG-plus tool system
1. Features of the BIG-plus tool system
The BIG-p lus tool system is fully compatible with the existing 7:24 shank taper. It distributes the amount of clearance between the spindle end face and the tool flange to each half of the spindle and the shank, respectively lengthening the spindle and thickening the shank flange. The size of the spindle end face and the tool flange. As shown in Figure 4, Figure 4a shows the ISO7388/1 holder combined with the BIG-plus tool system, and Figure 4b shows the MAS BT holder combined with the BIG-plus tool system.
The working principle of the Big-plus tool system is that the clearance of the end face when the tool shank is loaded into the spindle (before locking) is small. After the locking, the elastic expansion of the inner hole of the spindle is used to compensate the gap, and the expansion of the spindle hole is caused by the expansion of the shank. The tool moves axially and the shank is in close contact with the end face of the spindle.
2. Selection of BIG-plus tool system
Since the clearance of the end face when the shank is loaded into the spindle (before locking) is small (the shank clearance of No. 40 is 0.02 mm ± 0.005 mm). After locking, the elastic expansion of the inner bore of the spindle compensates for the gap, so that the shank and the end face of the spindle are tightly attached, so the BIG-plus tool system has the following advantages:
The contact area between the shank and the main shaft is increased to increase the rigidity and improve the vibration damping effect. The correction of the end face improves the repeatability of the automatic tool change, and the positioning of the end face stabilizes the axial dimension.
Compared with the BT taper shank, the load capacity of the Big-plus taper shank on the bending moment is increased by an increased support diameter, which increases the clamping stability. The Big-plus tool system has a high clamping rigidity, which reduces the runout of the tool holder during high-speed machining and improves the accuracy of repeated tool change.
However, the Big-plus tool holder must be strictly controlled to control the axial position accuracy of the tapered surface reference line and the flange end surface. The corresponding spindle must also control this axial precision, making the manufacturing process difficult. One point is even higher than the HSK tool holder requirements. The comparison between the BT holder and the Big-plus holder is shown in Figure 5.
Features and selection of Coromant Capto tool system
1. Features of the Coromant Capto tool system
The Coromant Capto tool system is shown in Figure 6. The tool system is centered by a triangular pyramid and is clamped from the inside of the triangular pyramid to make the end face fit snugly.
Its interface resembles a triangular pyramid. Thanks to the double-sided contact and the interference fit, the flange face is ground and ground with a triangular pyramid for good stability. The triangular pyramid interface is pre-tightened for high-precision grinding.
The Capto tool system adopting the polyhedral structure has the following features: The structure eliminates the transmission keyway structure, and the torque transmission is realized by the polyhedron, so there is no problem of stress concentration of the transmission key, and the dynamic balance problem caused by the key and the keyway is eliminated. In addition, since there is no transmission key, the cutting torque is evenly distributed, thereby increasing the torsional rigidity. The three transmission torque surfaces of the Capto tool system are shown in Fig. 7.
As for the skew comparison due to simple bending, the Capto tool system has demonstrated its superior performance. The Capto tool system has a longer taper, a smaller taper angle, more material and a higher clamping force, resulting in higher bending stiffness.
2. Selection of Coromant Capto tool system
Coromant Capto's innovative technology has three main points: it is the basis for quick change of the cutting unit on the lathe; it is the basis for the built-in rotary interface on the machine spindle; it is also a great way to optimize the tool to suit various applications.
This tool system can be used for turning, but also for boring and milling. It is a versatile tool system. Its four-lobed gripper groove is used for automatic tool change and the positioning slots required when the tool requires angular positioning, such as some turning applications. The cutting fluid is supplied from the inside, and the cutting fluid passes through the spindle directly to the cutting edge. High-pressure cooling is also an option. At the same time, the spindle with the Coromant Capto interface is also a very important feature for rotating the tool. Due to the better performance of this type of interface, more and more machine tool manufacturers have chosen it as the standard choice for machine tool interfaces. At present, Capto has formed an international standard (ISO 26623). However, the triangular pyramid of the Capto tool system, especially the spindle triangular pyramid hole, is difficult to process, so the processing cost is high and it is incompatible with the existing tool system, and the cooperation will be self-locking.
The structure comparison of the above four tools is shown in Table 4.
Conclusion
In view of the structural characteristics and working principle of the four tool systems used in high-speed milling, this paper introduces the selection requirements and applicable occasions of these four tool systems. The HSK tool system mainly depends on the maximum speed of the spindle and the structure of the tool holder. The characteristics and carrying capacity, the popularity of the tools and accessories, etc. to select the model and specifications of the HSK tool system, its use range is very wide; due to the KM tool system's tension and locking force, the performance of the KM tool system Better, but due to patent protection, KM tool system has been promoted and applied only on certain types of machine tools in the United States and Japan. There are not many domestic applications. Currently, KM tool systems are mainly used in Mori Seiki, Okuma, Daewoo mazak and Tsugami. On the machine of the same brand; the BIG-plus tool system is fully compatible with the existing 7:24 shank taper, does not add additional tool costs, has obtained German patents, and many tool manufacturers in Germany and Switzerland have been Production license; Capto tool system uses a polyhedral structure to produce higher bending stiffness, this tool system is available High-speed milling, may also be used for boring, turning, it is a versatile tool system.
In fact, the tool system is usually purchased as an accessory with a random bed and can be used for a long time, it is depreciated together with a random bed, which means that it is a one-time investment. Studies have shown that tool systems also cost less than 0.45% of total processing costs. Therefore, it is not worthwhile to reduce the processing cost by reducing the cost of the tool system. Selecting a high-quality tool system will achieve a multiplier effect in cutting.
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