High-speed machining has become a crucial and evolving aspect of modern manufacturing technology. Many industrialized nations have already adopted high-speed cutting machines with spindle speeds reaching tens of thousands of revolutions per minute. China's automotive, tractor, aerospace, and other industries have imported numerous advanced production lines, machining centers, and high-performance machine tools from abroad, including many high-speed cutting systems. As spindle speeds increase significantly, the performance of traditional BT (7:24 taper) tool systems struggles to meet the demands of high-speed cutting. In response, developed countries have raced to develop new tool systems suitable for high-speed cutting. Among these, the HSK (Hohl Schaft Kegel) system from Germany, the KM system from the US, and the NC5 system from Japan are widely used. The HSK system is the most mature and widely applied.
The HSK tool system uses a hollow short-cone structure and a two-sided clamping method, offering superior rigidity, radial runout accuracy, repeated installation accuracy, and clamping reliability. The precision of the tool system directly affects its performance. This paper analyzes the main differences between the German DIN standard and the ISO standard in the HSK tool system, discussing the impact of positioning accuracy and connection stiffness on the system's performance, aiming to provide guidance for the development of domestic tool systems.
The formulation of the HSK tool system standard began in 1987, with a special working group established at Achen University of Technology by over 30 units, including machine tool laboratories, manufacturers, and users. Professor Weck initiated the research and development of a new tool system. After the first round of research, the group submitted a proposal for "automatic tool change hollow handle" to the German Industrial Standards Organization in July 1990. In July 1991, Germany published the draft DIN standard for the HSK tool system and proposed the development of relevant ISO standards. In May 1992, ISO/TC29 decided not to formulate an ISO standard for automatic tool change hollow shanks. Following further studies, Germany officially established the DIN 69893 standard for the HSK tool system in 1993. In May 1996, at the ISO/TC29/WG33 review meeting, the HSK tool system based on DIN 69893 was developed into the ISO/DIS 12164 draft. After multiple revisions, the official ISO 12164 standard for the HSK tool system was issued in 2001.
Before the official ISO standard for the HSK tool system was promulgated, products were designed and manufactured according to the German DIN 69893 and DIN 69063 standards. However, the ISO standard introduced several important improvements. These differences significantly affect the performance of the HSK tool system. The quality of the taper between the shank and the spindle directly impacts its performance and accuracy. Therefore, setting appropriate accuracy requirements for the shank taper and spindle hole is critical. The DIN and ISO standards adopt different approaches to this issue.
For example, the HSK-A shank's main control dimensions under the DIN standard are shown in Figure 1, with Table 1 providing the relevant dimensions for the HSK-A63 shank and spindle taper. The tolerance zones for the shank and spindle tapers under the DIN standard are also illustrated. According to the DIN standard, the small end diameter D3 is calculated as *D3max = D2max - 2*L3*tg(2°51'45" - AT3/2) = 46.534 mm and *D3min = D2min - 2*L3*tg(2°51'45") = 46.529 mm. The interference at the large and small ends is also detailed.
Under the ISO standard, the main control dimensions of the HSK-A shank and spindle taper are shown in Figure 3. The ISO standard controls the taper using the large end diameter d2, section position dimension l2, profile tolerance t, and taper (1:9.98). The small end is not specified separately. The corresponding spindle taper hole control method is similar, but the taper is still 1:10. The ISO standard does not specify L3, D3, or related dimensions. The tolerance zones for the HSK-A shank and spindle taper are shown in Figure 4, with the limit dimensions calculated accordingly.
When comparing the DIN and ISO standards, it is evident that the ISO standard provides larger interference at the large end (17 μm max, 7 μm min) compared to the DIN standard (12 μm max, 4 μm min). This results in higher coupling stiffness and better performance under heavy loads. Additionally, the ISO standard ensures more stable system performance due to smaller variations in interference fit.
In conclusion, the HSK tool system based on the ISO standard offers greater interference between the tool holder and spindle taper hole, enhancing positioning accuracy and system stability. The use of different control tapers (1:9.98 and 1:10) for the shank and spindle under the ISO standard is reasonable, promoting the high rigidity of the HSK system. Under sufficient clamping force, the ISO-standard HSK system is more suitable for heavy load cutting. On the other hand, the DIN-standard HSK system has smaller interference, ensuring reliable clamping and better performance for high-speed, light-load applications.
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